Molten salt membrane electrolyzer

ABSTRACT

A molten salt, membrane electrolyzer apparatus may include an anolyte compartment containing a molten salt anolyte comprising primarily chloride salts and a lithium carbonate (Li2CO3) feed material. A first and second electrode assemblies each having respective anodes, cathode housings proximate the first anode within the anolyte compartment and in fluid contact with the molten salt anolyte and having a primary transfer portion comprising a porous membrane and cathodes positioned within the first catholyte compartment so that the primary transfer portion is disposed between respective anode and cathode. A power supply can be configured to apply an electric potential between the first anode and the first cathode that is sufficient to initiate electrolysis of lithium carbonate and is greater than the electric potential required to initiate LiCl electrolysis.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. provisional patent application No. 62/878,444 filed on Jul. 25, 2019, the entirety of which is hereby incorporated by reference.

FIELD OF THE INVENTION

In one of its aspects, the present invention relates to molten salt electrolysis, and in particular an electrolyzer apparatus for molten salt electrolysis and a process for producing lithium metal from lithium carbonate.

INTRODUCTION

Molten salt electrolysis has been widely practiced for over a hundred years, including the Hall-Heroult process for aluminum, the Dow and IG Farben processes for magnesium, and the Downs process for alkali metals. The majority of commercial-scale molten salt electrolytic processes use chloride or fluoride electrolytes, as these are solvents which facilitate the electrowinning of the target metals from their oxides, chlorides, or other compounds. In many cases, the electrolyte, or the oxide, chloride, or fluoride of the desired product metal, have either physical properties that are undesirable (e.g., toxic, hygroscopic, corrosive, etc.) or are disadvantageous for other reasons (cost, availability, security of supply, competing uses, difficulty of manufacture, etc.).

U.S. Pat. No. 3,607,684 discloses a process for the manufacture of alkali metal by passing an electroyzing current from an anode to a cathode. The anode is in contact with a fused metal halide salt comprising ions of the alkali metal and no other monovalent cations. The cathode is in the form of liquid alkali metal. Interdisposed between the anode and the cathode is a diaphragm. The diaphragm is polycrystalline ceramic material which has ions of the alkali metal or ions capable of being replaced by the alkali metal. The diaphragm is permeable only to monovalent cations and therefore will pass only the cations of the alkali metal which is being manufactured. Halogen can be recovered as the anode product or a halogenated hydrocarbon can be recovered as the anode product by introducing a hydrocarbon or partially halogenated hydrocarbon into the anode compartment.

U.S. Pat. No. 1,501,756 discloses a process of producing alkali metals and halogens by electrolysis of fused halide baths, as for example, sodium chloride. An object of the invention is to recover halogens containing practically no gaseous impurities.

U.S. Pat. No. 4,988,417 discloses A method of electrolytically producing lithium includes providing an electrolytic cell having an anode compartment and a cathode compartment. The compartments are separated by a porous electrically nonconductive membrane which will be wetted by the electrolyte and permit migration of lithium ions therethrough. Lithium carbonate is introduced into the anode compartment and produces delivery of lithium ions from the anode compartment to the cathode compartment where such ions are converted into lithium metal. The membrane is preferably a non-glass oxide membrane such as a magnesium oxide membrane. The membrane serves to resist undesired backflow of the lithium from the cathode compartment through the membrane into the anode compartment. Undesired communication between the anode and cathode is further resisted by separating the air spaces thereover. This may be accomplished by applying an inert gas purge and a positive pressure in the cathode compartment. The apparatus preferably includes an electrolytic cell with an anode compartment and a cathode compartment and an electrically nonconductive membrane which is wettable by the electrolyte and will permit migration of the lithium ion therethrough while resisting reverse passage of lithium therethrough.

SUMMARY

Lithium metal can be produced using a modified Downs cell (see, for example, U.S. Pat. Nos. 1,501,756 and 6,063,247) from a eutectic mixture of LiCl—KCl using a LiCl feed material. The Downs cell generally uses bottom-mounted graphite anodes and side-mounted cathodes in a refractory-lined cell, typically comprising four connected anode and cathode assemblies arranged in a known, “cloverleaf” pattern. Interposed between the anode and cathode is a metal mesh, which serves to separate the anode gases from the cathode product, thus limiting recombination of the two products.

Under the influence of sufficient potential, molten lithium metal plates out onto the cathode, while chlorine gas evolves at the anode, according to reaction 1 (below). The metal floats upwards where it is collected in an annular bell submerged in the electrolyte. The bell directs the molten metal out of the cell due to differential metallostatic head produced by the difference in density between the electrolyte and the metal. Chlorine gas evolves at the anode as a result of the electrolytic reaction and is captured above the anode. Back-reaction of the metallic and gaseous products is prevented by a wire mesh interposed between the two electrodes.

2LiCl(l)=2Li(l)+Cl₂(g); E ^(o)=−3.609 V   [1]

One of the drawbacks of the Downs process is that LiCl is hygroscopic, which makes its handling challenging and, even when well done, it can act as a source of water in the electrolytic cell. Water in a Downs cell has several negative consequences. Firstly, it reacts with the lithium chloride, making HCl and LiOH. LiOH has low solubility in the melt, which can cause it to form sludge and potentially results in lithium losses. Secondly, water attacks the graphite anodes, causing the anodes to oxidize and erode. This is problematic, because the anode in a Downs cell cannot be replaced without rebuilding the cell, which can increase direct costs and downtime/lost production. Thirdly, while dry chlorine gas can be handled in conventional materials, wet chlorine gas is highly corrosive to the interior of the cell and downstream equipment. This means that these components must be made of special corrosion-resistant steels, and even these do not necessarily have long life. This can have serious negative consequences for equipment availability. Another drawback of the Downs process may be that the relatively low quality of the chlorine gas produced means it has limited value as a by-product, and thus is generally treated as a toxic waste gas. This can impose additional costs on the operation of the Downs, thereby increasing the cost of the lithium product. In addition, because the LiCl required by the Downs process must be of high purity, it is often derived from high purity lithium carbonate. Conversion of lithium carbonate to LiCl is a costly process, requiring consumption of HCl and drying under vacuum. As a result, LiCl tends to be a costlier source of lithium feed material than lithium carbonate (Li₂CO₃).

In GB1024689, a method is described that attempts to reduce the reliance of the Downs process an LiCl feed. The method proposes feeding a small quantity of Li₂CO₃ directly into the anode compartment where it reacts in solid form with the evolved chlorine gas. This, however, may not be a practical approach, for a number of reasons. Firstly, because Li₂CO₃ is not an easily flowing bulk solid, it becomes sticky at the typical Downs cell operating temperatures. This means that gas permeability can be difficult to maintain, and a crust can form in due course, resulting in relatively poor conversion of the Li₂CO₃. Secondly, Li₂CO₃reacts at the cathode with lithium metal, and is directly electrolyzed according to reactions 2 and 3 (below). This may cause reductions in current efficiency, elemental carbon sludge formation, and low-solubility Li₂O formation whenever there is a mismatch between the feeding and consumption of Li₂CO₃. Such mismatches can occur for operational reasons, such as current setpoint changes, feed system lag, power fluctuations, or the aforementioned crusting. These challenges make the proposed method of GB1024689 difficult to adopt for the commercial production of lithium metal from Li₂CO₃.

4Li(l, s)+Li₂CO₃(l, s)=C(s)+3Li₂O(l, s)   [2]

3CO₃ ²⁻(l)=2CO₂(g)+C(s)+3O²⁻(l); E ^(o)=˜−2.5 V   [3]

U.S. Pat. No. 4,968,417 describes a molten salt LiCl—KCl electrolytic process whereby lithium carbonate is fed into a cell with separate anolyte and catholyte compartments. The cell is separated by a porous ceramic membrane. According to the disclosure, the cell is intended to be operated between 550-770° C., with 5-10% Li₂CO₃ dissolved in the melt, while carbon anodes provide a source of carbon for the reduction reaction. Beneficially, the cell of the invention is able to produce relatively high purity lithium metal from lithium carbonate, according to equation 4, which has a lower decomposition potential than the conventional chloride reaction 1, thereby nominally reducing the energy consumption and cost thereof.

Li₂CO₃(s, l)+1/2C(s)=2Li(l)+3/2CO₂(g); E ^(o)=−2.127 V   [4]

While it is true that relying on reaction 4 reduces the decomposition potential of the lithium metal-producing reaction, there are a number of practical limitations that can negate this benefit. Porous membranes not only reduce diffusion, they also have substantially higher resistance to ionic condition. Typically, this can be 4-10 times higher than the electrolyte bath, meaning that membranes of a workable thickness can more than double the resistive losses due to the anode-to-cathode gap. Also, because the carbon anodes are consumed by the process, the electrical resistance of the anode-to-cathode gap increases over time, leading to further increases to the resistive losses as the anode wears.

One or more of these effects may be mitigated to some extent by operating at low current density, which generally lead to a low productivity per unit electrode area. This can have the effect of increasing the overall physical size of the electrolysis unit, and/or the number of cells required for a given production capacity, which can increase the capital cost and personnel costs of the plant.

Operation at low current density may also require a relatively larger membrane area, which may tend to increase carbonate transport between the anolyte and catholyte. This can result in reduced current efficiency and the production of elemental carbon sludge and Li₂O build-up in the cathode compartment, further reducing the economic performance of the cell.

Another consequence of operating at low applied potential is that the process relies entirely on a carbon-consuming reaction. This can result in a high carbon consumption per unit of metal produced which, given the high cost of graphite, can increase the operating cost of the plant.

In “The Electrowinning of Lithium from Chloride-Carbonate Melts”, Kruesi and Fray disclose a similar low-potential Li₂CO₃ electrolysis process to U.S. Pat. No. 4,988,417. Efforts are made to reduce carbon costs by employing a durable anode and a preferentially-consumed bed or slurry of low-cost carbon. Although most of the carbon anode approaches reported by Kruesi and Fray are successful at producing lithium metal, few do so with high current efficiency, and none achieve more than a modest reduction in carbon consumption. Also, because the work continues to use low applied potentials in an effort to realize energy savings, it is limited to low current-density operation.

Current electrolyzer technology has not been adapted to the membrane processes described above at industrially practical scale. With the Downs cell, its non-contiguous membrane and bottom-mounted anode make adaptation difficult. Replacing the steel mesh membrane with a porous membrane is not generally practical, as, for example, it would be difficult to ensure a leak-tight seal against the bottom of the vessel, thereby preventing effective separation of the anode and cathode compartments. Also, because the anodes are bottom mounted, the life of the vessel could be limited to less than a week or two before the anode would have to be replaced.

Hall-Heroult cells have been well developed for aluminum electrolysis with consumable anodes; however, these are designed for operation with a metal that is denser than the electrolyte and so are not suitable for the lithium production processes described herein.

While the Dow magnesium electrolyzer may be designed for both consumable anodes and metal with lower density than the electrolyte, it is generally impractical to provide feeding mechanisms that are capable of supplying each individual sub-compartment with Li₂CO₃, feed material while accommodating the anode mechanism, without unduly enlarging the anode-to-cathode distance and incurring the attendant resistive losses and heat balance problems. Additionally, an arrangement where each anode is in an independent compartment and the cathodes are in a common compartment leaves the electrolyzer vulnerable to membrane failure, as leakage in any single membrane contaminates all cathodes.

U.S. Pat. No. 3,607,684 discloses a membrane electrolyzer with a beta-alumina diaphragm and a solvent metal cathode. This process has drawbacks when used with Li₂CO₃, including that the proposed membranes are located on the bottom of the vessel in a “window pane” arrangement. Such an arrangement would be difficult to execute without leaks, given the substantial thermal expansion of components between assembly and operating temperatures. Also, it is known that molten alloys of lithium are relatively aggressive towards alumina, meaning that the membranes would be attacked by the flowing metal and any likely gasket materials, limiting the life of the electrolyzer substantially.

Despite the advances made to date in the development molten salt electrolysis devices, there is significant room for improvement to address the above-mentioned problems and shortcomings of the prior art.

It may be an object of the present invention to obviate or mitigate at least one of the above-mentioned disadvantages of the prior art, and to provide a novel molten salt electrolyzer apparatus. For example, the teachings described herein may be related to an improved process and apparatus/equipment for the production of lithium metal from lithium carbonate. To help facilitate relatively large-scale production of lithium metal, the process and equipment/apparatus described herein may preferably have one or more of the following: i) relatively high specific productivity, ii) relatively high availability, iii) relatively high metal recovery, iv) relatively high lithium metal product purity, v) relatively low operating costs and vi) a generally acceptable specific energy use.

In accordance with one broad aspect of the teachings described herein a process for producing lithium metal from lithium carbonate using an electrolyzer apparatus having a containment vessel defining an anolyte compartment containing a first anode and a second anode submerged in a common anolyte bath comprising chloride salts can include: a) providing a first cathode housing in the anolyte bath proximate the first anode, the first cathode housing may define a first catholyte compartment containing a first cathode and a molten salt catholyte and may be at least partially bounded by a first primary transfer portion disposed between the first cathode and first anode and comprising a first porous membrane configured to permit migration of lithium ions and resist migration of carbonate ions; b) providing a second cathode housing in the anolyte bath proximate the second anode, the second cathode housing may define a second catholyte compartment containing a second cathode and the molten salt catholyte and may be at least partially bounded by a second primary transfer portion disposed between the second cathode and second anode and comprising a second porous membrane configured to permit migration of lithium ions and resist migration of carbonate ions; c) introducing a lithium carbonate feed material into the anolyte bath; d) applying an electric overpotential that is sufficient to initiate electrolysis of lithium carbonate feed material and is greater than an electric potential required to initiate electrolysis of lithium chloride (e.g. is substantially greater than the equilibrium potential of lithium chloride) between the first anode and the first cathode and between the second anode and the second cathode, thereby electrolyzing the lithium carbonate feed material; d) transferring lithium ions from the anolyte bath into the first catholyte compartment through the first primary transfer portion and resisting the transfer of carbonate ions from the anolyte bath into the first catholyte compartment; e) transferring lithium ions from the anolyte bath into the second catholyte compartment through the second primary transfer portion and resisting the transfer of carbonate ions from the anolyte bath into the second catholyte compartment; and f) converting the lithium ions into lithium metal.

The process may include introducing chlorine gas into the first catholyte compartment via a chlorine delivery system, reacting the chlorine gas with the lithium carbonate to form lithium chloride (LiCl) and carbon dioxide, and electrolyzing the lithium chloride.

A carbonate ion concentration in the catholyte within the first catholyte compartment may be less than in the anolyte bath.

A carbonate ion concentration in first catholyte compartment may be less than about 100 ppm.

The process may include inhibiting carbon and/or lithium oxide fouling of the first cathode by introducing chlorine gas into the catholyte in the first cathode compartment.

The process may include maintaining a current density of between about 0.75 A/cm² and about 4 A/cm² between the first anode and first cathode and between the second anode and second cathode.

The current density may be at least about 1.2 A/cm².

The process may include maintaining a concentration of lithium carbonate of at least 0.1 mol % in the anolyte bath.

The process may include maintaining a concentration of lithium carbonate of at least 0.5 mol % in the anolyte bath.

The process may include extracting anode gases generated proximate the first anode via an anode gas extraction apparatus and introducing additional lithium carbonate feed material into the anolyte bath when a concentration of chlorine gas in the anodes gases exceeds a predetermined monitoring threshold.

A quantity of carbon that is required per unit of lithium metal produced may be less than about 0.4 kg C/kg Li.

The process may include maintaining at least one of the anolyte and the catholyte at a temperature that is greater than about 375° C. and/or about 400° C.

The process may include maintaining the at least one of the anolyte and the catholyte at a temperature that is between about 450° C. and about 650° C.

The anolyte and the catholyte may each include molten LiCl and KCl.

The electrolyzer apparatus may include a first cathode mounting apparatus extending over an open upper end of the containment vessel and supporting at least the first cathode. The first cathode mounting apparatus may be removable from the containment vessel and the first cathode may be removed with the first cathode mounting apparatus while the anolyte bath remains contained within the anolyte compartment.

The first cathode mounting apparatus may include a first feed port through which lithium carbonate is introduced into the anolyte bath. Removing the first cathode mounting apparatus may simultaneously remove the first cathode and the first feed port from the containment vessel.

In accordance with another broad aspect of the teachings described herein, a molten salt, membrane electrolyzer apparatus for the production of lithium metal from lithium carbonate via an electrolysis process may include a containment vessel defining an anolyte compartment containing a molten salt anolyte bath comprising chloride salts and a lithium carbonate (Li₂CO₃) feed material. A first electrode assembly may include a first anode extending into the anolyte compartment and in fluid contact with the molten salt anolyte bath and a first cathode housing proximate the first anode within the anolyte compartment and in fluid contact with the molten salt anolyte bath. The first cathode housing may define a first catholyte compartment containing a molten salt catholyte including chloride salts and being at least partially bounded by a primary transfer portion comprising a first porous membrane configured to permit migration of lithium ions and resist migration of carbonate ions from the anolyte compartment into the first catholyte compartment. A first cathode may be provided within the first catholyte compartment, in fluid contact with the catholyte and positioned so that the primary transfer portion is disposed between the first anode and the first cathode. A second electrode assembly may include a second anode extending generally into the anolyte compartment and in fluid contact with the molten salt anolyte bath and a second cathode housing proximate the second anode within the anolyte compartment and in fluid contact with the molten salt anolyte bath. The second cathode housing may include a second catholyte compartment containing a molten salt catholyte including chloride salts and being at least partially bounded by a primary transfer portion comprising a second porous membrane configured to permit migration of lithium ions and resist migration of carbonate ions from the anolyte compartment into the second catholyte compartment. A second cathode within the second catholyte compartment may be in fluid contact with the catholyte and may be positioned so that the second primary transfer portion is disposed between the second anode and the second cathode. A power supply may be configured to apply an electric potential between at least the first anode and the first cathode that that is greater than the electric potential required to initiate electrolysis of the lithium carbonate feed material and is greater than the electric potential required to initiate electrolysis of lithium chloride.

The containment vessel may include an open upper end and the first anode, first cathode, second anode and second cathode may extend downwardly through the open upper end into the anolyte bath.

The electric potential between the first anode and the first cathode may be at least 4V.

The electric potential between the first anode and the first cathode may be at least 7V and may be about 10V.

The electric potential between the first anode and the first cathode may be at least 10V.

The first electrode assembly may operate at current density of between bout 1 A/cm² and about 4 A/cm².

The first electrode assembly may operate at current density of about 1.2 A/cm².

The first anode may include a generally planar plate having a first anode active surface facing the first cathode, and the first cathode may include a generally planar plate that is substantially parallel to the first anode and having a first cathode active surface opposite and facing the anode active surface.

The first cathode active surface may be between about 50% and about 200% of the first anode active surface, and preferably may be between about 80% and about 120% of the anode active surface, and more preferably may be substantially the same as the anode active surface.

The second electrode assembly may be adjacent the first electrode assembly such that the first cathode is disposed between and is generally equally spaced between the first anode and the second anode. An electric potential that is sufficient to initiate electrolysis of lithium carbonate and is greater than the electric potential required to initiate LiCl electrolysis may be applied between the first cathode and the second anode.

The first cathode housing may include a secondary transfer portion disposed between the first cathode and the second anode and may include a porous membrane to permit migration of lithium ions from the anolyte compartment into the first catholyte compartment and resisting the migration of carbonate ions from the anolyte compartment into the first catholyte compartment.

The first cathode housing may be formed at least substantially entirely from the porous membrane.

At least some regions of the first cathode housing outside the primary transfer portion and the secondary transfer portion may be treated to inhibit the transmission of ions through the regions of the first cathode housing outside the primary transfer portion and the secondary transfer portion.

The least some regions of the first cathode housing outside the primary transfer portion and the secondary transfer portion may be coated or impregnated with an ion blocking material.

The first cathode housing may be formed at least substantially entirely from the porous membrane.

At least some regions of the first cathode housing outside the primary transfer portion may be treated to inhibit the transmission of ions through the regions of the first cathode housing outside the primary transfer portion.

The at least some regions of the first cathode housing outside the primary transfer portion may be coated or impregnated with an ion blocking material.

The porous membrane may be formed from a ceramic material and having an average pore size of between about 0.1 and about 100 microns.

A concentration of carbonate ions within the first catholyte compartment may be less than about 100 ppm while the apparatus is in use.

A concentration of carbonate ions within the first catholyte compartment may be less than a concentration of carbonate ions within the anolyte compartment.

The first anode may be removable from the anolyte compartment independently of the first cathode housing and the first cathode.

The first anode may be removable from the anolyte compartment independently of the second anode.

The first anode may be removable from the anolyte compartment without draining the molten salt anolyte bath from the anolyte compartment.

A chlorine delivery system may be configured to introduce chlorine gas into the first catholyte compartment while the apparatus is in use.

The chlorine gas may react with Li₂CO₃ present within the first catholyte compartment to produce LiCl and carbon dioxide, thereby inhibiting carbon and/or lithium oxide fouling of the first cathode.

The chlorine gas may react with excess lithium within the first catholyte compartment thereby inhibiting damage to the membrane.

A gas extraction apparatus may be configured to capture product gases formed adjacent the first anode and convey the product gases away from the containment vessel.

The anolyte bath may be at a temperature of between about 450° C. and about 700° C. degrees Celsius.

The anolyte bath may be at a temperature of between about 475° C. and about 650° C.

The first electrode assembly may include an anode mounting apparatus extending over the upper end of the containment vessel in a first direction and from which the first anode is suspended. The anode mounting apparatus may be detachable from the containment vessel whereby the first anode is removed from the anolyte compartment.

The first anode may be detachably connected to the anode mounting apparatus.

The anode mounting apparatus may include an electrical connector that electrically connects the first anode to the power supply when the anode mounting apparatus is attached to the containment vessel. The electrical connection between the first anode and the power supply may be interrupted when the anode mounting apparatus is detached from the containment vessel.

The anode mounting apparatus may include an insulating layer disposed between the anolyte chamber and the electrical connector to inhibit heat transfer from the molten salt anolyte bath to the electrical connector when the apparatus is in use. The insulating lining may be removable with the anode mounting apparatus.

The anode mounting apparatus may include a gas extraction apparatus having a gas capture hood positioned above the first anode and configured to capture product gases formed adjacent the first anode and bubbling out of the molten salt anolyte bath and a gas removal conduit extending from the gas capture hood and configured to convey the product gases away from the containment vessel. At least a portion of the gas extraction apparatus may be removable with the anode mounting apparatus.

The gas capture hood may be electrically isolated from the first anode.

The first electrode assembly may include a cathode mounting apparatus extending over the upper end of the containment vessel in the first direction and from which the first cathode is suspended. The cathode mounting apparatus may be detachable from the containment vessel whereby the first cathode is removed from the containment vessel with the cathode mounting apparatus.

The first cathode housing may be suspended from the cathode mounting apparatus whereby the first cathode housing is removed from the containment vessel with the cathode mounting apparatus.

The cathode mounting apparatus may include a lithium extraction assembly that includes a lithium extraction conduit that extends from an upper end proximate the cathode mounting apparatus to a lower end that disposed within the first catholyte compartment to extract lithium metal that collects in the catholyte. The lithium extraction conduit may be removed from the containment vessel with the cathode mounting apparatus.

The cathode mounting apparatus may include an electrical connector that electrically connects the first cathode to the power supply when the cathode mounting apparatus is attached to the containment vessel. The electrical connection between the first cathode and the power supply may be interrupted when the cathode mounting apparatus is detached from the containment vessel.

At least one feed port may be provided in the cathode mounting apparatus through which the feed material can be introduced into the anolyte compartment.

The at least one feed port may be removable from the containment vessel with the cathode mounting apparatus.

A plurality of cathode mounting apparatuses and anode mounting apparatuses may be in an alternating arrangement. Adjacent ones of the cathode mounting apparatuses and anode mounting apparatuses may cooperate to cover substantially the entire upper end of the containment vessel.

A filling tube may fluidly connect the anolyte compartment and the first catholyte compartment whereby anolyte from the anolyte bath can be drawn into the first catholyte compartment when a vacuum is applied to the first catholyte compartment.

Li₂CO₃ within the anolyte bath may react with Cl₂ produced within the anolyte compartment, thereby converting it to LiCl, CO₂ and O₂ and supressing the emission of Cl₂ from the containment vessel.

A quantity of carbon required per unit of lithium metal produced may be less than about 0.4 kg C/kg Li.

A concentration of dissolved lithium carbonate in the anolyte within the anolyte compartment may be greater than 0.1 mol %.

The concentration of dissolved lithium carbonate concentration of dissolved lithium carbonate in the anolyte within the anolyte compartment may be greater than 0.5 mol % and may be about 1 mol % or greater.

A CO2/O2 ratio in an off-gas from the anolyte compartment may be between about 2 and about 2.5.

The first porous membrane may have a maximum pore size of about 1 micron and average pore size less than about 0.5 microns.

The first porous membrane may have an open porosity of between 10-80%, and more preferably between 30-60%.

The first porous membrane may be substantially rigid.

The apparatus may include a third electrode assembly including a third anode extending into the anolyte compartment and in fluid contact with the molten salt anolyte bath and a third cathode housing proximate the third anode within the anolyte compartment and in fluid contact with the molten salt anolyte bath. The third cathode housing may define a third catholyte compartment containing a molten salt catholyte comprising chloride salts and being at least partially bounded by a primary transfer portion comprising a third porous membrane configured to permit migration of lithium ions and resist migration of carbonate ions from the anolyte compartment into the third catholyte compartment. A third cathode may be provided within the third catholyte compartment, in fluid contact with the catholyte and positioned so that the primary transfer portion is disposed between the third anode and the third cathode.

The apparatus may include a fourth electrode assembly including a fourth anode extending into the anolyte compartment and in fluid contact with the molten salt anolyte bath and a fourth cathode housing proximate the fourth anode within the anolyte compartment and in fluid contact with the molten salt anolyte bath. The fourth cathode housing may define a fourth catholyte compartment containing a molten salt catholyte comprising chloride salts and being at least partially bounded by a primary transfer portion comprising a fourth porous membrane configured to permit migration of lithium ions and resist migration of carbonate ions from the anolyte compartment into the fourth catholyte compartment. A fourth cathode may be provided within the fourth catholyte compartment, in fluid contact with the catholyte and positioned so that the primary transfer portion is disposed between the fourth anode and the fourth cathode.

In accordance with yet another broad aspect of the teachings described herein, a molten salt, membrane electrolyzer apparatus for the production of lithium metal from lithium carbonate via an electrolysis process may include a containment vessel defining an anolyte compartment containing a molten salt anolyte bath, the anolyte bath comprising chloride salts and more than about 0.1 mol % lithium carbonate (Li₂CO₃) feed material, and a plurality of electrode assemblies spaced apart from each other and extending into the anolyte compartment. Each electrode assembly may include: a cathode housing in fluid contact with the molten salt anolyte bath. The cathode housing may define fining a catholyte compartment containing a molten salt catholyte including chloride salts and being at least partially bounded by a primary transfer portion including a porous membrane configured to permit migration of lithium ions and resist migration of carbonate ions from the anolyte compartment into the catholyte compartment. A cathode may be positioned within the catholyte compartment, in fluid contact with the catholyte and may have an active surface. An anode may be in contact with the molten salt anolyte bath and may be proximate the cathode housing. The anode may have an active surface that is substantially equidistant from the active surface of the cathode and may be positioned so that the primary transfer portion of the membrane is disposed between the active surface of the anode and the active surface of the cathode. A power supply may be configured to apply an electric potential to each electrode assembly that is greater than the electric potential required to initiate electrolysis of the lithium carbonate feed material.

The plurality of electrode assemblies may include at least ten electrode assemblies arranged in an array within the anolyte compartment.

The anode may include a substantially planar plate and the cathode may include a substantially planar plate that is parallel to the anode.

The primary transfer portion of porous membrane may be substantially planar and may be parallel to both the anode and the cathode.

At least a first and a second anode support apparatus may extend across an open upper end of the containment vessel and over the anolyte compartment. The first anode support apparatus may support at least a first anode and the second anode support apparatus may support at least a second anode.

The first anode support apparatus and the first anode supported thereon may be removable from the containment vessel independently from the second anode support apparatus.

The first anode support apparatus and the first anode supported thereon may be removable while the anolyte bath is contained within the anolyte compartment.

The first anode support apparatus may include an electrical connector that electrically connects the first anode to the power supply and wherein the electrical connection is interrupted when the first anode support apparatus is removed.

At least a first cathode support apparatus may be disposed between the first and second anode support apparatuses, and a second cathode support apparatus may be on an opposing side of the second anode support. Each cathode support apparatus may extend across the open upper end of the containment vessel and over the anolyte compartment. The first cathode support apparatus may support at least a first cathode proximate the first anode and the second cathode support apparatus may support at least a second cathode proximate the second anode.

The first cathode support apparatus and first cathode supported thereon may be removable from the containment vessel independently from the first anode support apparatus.

The first cathode support apparatus and first cathode supported thereon may be removable from the containment vessel while the anolyte bath is contained within the anolyte compartment.

The first cathode support apparatus may include an electrical connector that electrically connects the first cathode to the power supply and wherein the electrical connection may be interrupted when the first cathode support apparatus is removed.

A first cathode housing may surround the first cathode and may be suspended from the first cathode mounting apparatus whereby the first cathode housing may be removed from the containment vessel with the first cathode mounting apparatus.

The porous membrane may include a non-wetting ceramic material.

The non-wetting ceramic material may have an open porosity of between about 30% and about 60%.

A ratio of an area of the active surface of the anode to an area of the active surface of the cathode may be between about 0.5 and 2, and more preferably is between 0.8 to 1.2.

A chlorine delivery system may be configured to introduce chlorine gas into each catholyte compartment.

The chlorine gas may react with lithium carbonate present within the catholyte to product carbon dioxide and lithium chloride.

The porous membrane may have a maximum pore size of about 1 micron and average pore size less than about 0.5 microns.

The electric potential between the anode and the cathode may be at least 4V.

The electric potential between the anode and the cathode may be at least 7V and may be about 10V.

The electric potential between the anode and the cathode may be at least 10V.

Each electrode assembly ray operate at a current density of between about 1 A/cm² and about 4 A/cm².

Each electrode assembly may operate at a current density of about 1.2 A/cm².

The power supply may be configured to apply an electric potential to each electrode assembly that is greater than the electric potential required to initiate electrolysis of lithium chloride.

The anolyte bath may be at a temperature of between about 450° C. and about 700° C. degrees Celsius.

Thus, the present inventors have developed a molten salt electrolyzer apparatus for the production of alkali metals from suitable feed materials, and in particular may be useful for the production of lithium metal from lithium carbonate. The present electrolyzer apparatus can help facilitate the relatively large-scale economical production of lithium metal using Li₂CO₃ as a feed source. The use of its repeating, multi-unit arrangement within a single vessel of the electrolyzer apparatus described herein may help reduce the number of cells that need to be built in order to achieve large-scale production of metal, thereby reducing both the capital cost and maintenance labour burden, as compared to previously reported electrolyzers. The interleaving arrangement described herein may also help reduce (and optionally help minimize) the anode-to-cathode distance (ACD), which may help reduce the resistive heat losses incurred by the process, which may in turn help reduce the operating cost of the plant. Additionally, the electrolyzer apparatus described herein may be operated at relatively high current density, which may help contribute to achieving a relatively higher specific productivity (for example, as compared to previously reported electrolyzers). Furthermore, the top-mounted, self-contained arrangement of the anodes and cathodes can help facilitate the relatively simple removal and frequent exchange/repair of the electrodes (for example without having to drain the anolyte bath), thereby facilitating uninterrupted operation at high throughput. This again can help reduce the operating costs of an electrolyzer apparatus.

To the knowledge of the inventors, a molten salt electrolyzer apparatus with such a combination of features is heretofore unknown. Other advantages of the invention may become apparent to those of skill in the art upon reviewing the present specification.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will be described with reference to the accompanying drawings, wherein like reference numerals denote like parts, and in which:

FIG. 1a is a schematic representation of one example of an electrolyzer;

FIG. 1b is a schematic representation of one example of an electrode assembly;

FIG. 2 is a schematic representation of another example of an electrolyzer;

FIG. 3 is a plan view of another example of an electrolyzer;

FIG. 4 is a side elevation view of the electrolyzer of FIG. 3;

FIG. 5a is a plan section of the electrolyzer of FIG. 4, taken along line A-A;

FIG. 5b is an enlarged plan view of an anode mounting apparatus in FIG. 5a , through which line B-B passes;

FIG. 5c is an enlarged plan view of a cathode mounting apparatus in FIG. 5a , through which line C-C passes;

FIG. 6 is a split vertical transverse section of the electrolyzer of FIG. 5a , taken along line B-B, illustrating the end-on view of the anode on the left side of the split, and a section through the anode on the right side of the split;

FIG. 7 is a split vertical transverse section of the electrolyzer of FIG. 5a , taken along line C-C, illustrating the end-on view of the cathode on the left side of the split, and a section through the cathode on the right side of the split;

FIG. 8a is a split vertical transverse section of a portion of the electrolyzer of FIG. 5b , taken along line B-B;

FIG. 8b is a longitudinal section of the anode beam of FIG. 8a taken along line 8 b-8 b;

FIG. 9a is a split vertical transverse section of a portion of the electrolyzer of FIG. 5a , taken along line C-C;

FIG. 9b is a longitudinal section of the cathode beam of FIG. 9a , taken along line 9 b-9 b;

FIG. 10 is a section of the electrolyzer of FIG. 3 through four anode and cathode assemblies;

FIG. 11a is a split vertical transverse section of another example of an electrolyzer;

FIG. 11b is a longitudinal section of the anode beam of FIG. 11 a, taken along line 11 b-11 b; and

FIG. 12 is a plot of current density, voltage and gas analysis vs time for the operation of one example of an electrolyzer.

DETAILED DESCRIPTION

Various apparatuses or processes will be described below to provide an example of an embodiment of each claimed invention. No embodiment described below limits any claimed invention and any claimed invention may cover processes or apparatuses that differ from those described below. The claimed inventions are not limited to apparatuses or processes having all of the features of any one apparatus or process described below or to features common to multiple or all of the apparatuses described below. It is possible that an apparatus or process described below is not an embodiment of any claimed invention. Any invention disclosed in an apparatus or process described below that is not claimed in this document may be the subject matter of another protective instrument, for example, a continuing patent application, and the applicants, inventors, or owners do not intend to abandon, disclaim, or dedicate to the public any such invention by its disclosure in this document.

Molten salt electrolysis and electrolyzers can be used in the production of metals from oxide, nitrate, sulfate, or carbonate compounds, Novel electrolyzer apparatuses described herein include a containment vessel that is configured to contain a molten salt anolyte (and function as an anolyte chamber) and to have at least one electrode assembly and preferably having at least two electrode assemblies (each having an anode and a complimentary cathode) positioned within the containment vessel. Optionally, a single containment vessel (preferably with a single anolyte bath) may have 2 or more electrode assemblies (electrode pairs), and may have at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or more electrode assemblies. In some preferred embodiments the containment vessel may include at least 10 electrode assemblies.

The electrolyzer apparatuses described herein are preferably configured such that the anodes are each directly submerged within the common, molten salt anolyte bath while each cathode is surrounded by a suitable cathode housing to provide a respective, discrete catholyte compartment proximate each cathode. This can provide an apparatus that includes a common anolyte compartment in combination with a plurality of discrete catholyte compartments. Configuring the apparatus in this manner may help enhance the resilience of the apparatus and/or help reduce downtime and/or help facilitate maintenance and repair of the apparatus, For example, in this arrangement a failure or fouling of any one membrane or cathode housing by, for example, cracking or prolonged lithium metal attack, will only tend to affect the production from one electrode pair. This may help provide redundancy for the electrolyzer apparatus, as it may continue to be successfully operated even with several compromised membranes in some examples. In addition, in the event of failure, or the accumulation of electrolyzed carbon or other insoluble build-up, a given membrane can be removed, repaired and/or replaced without substantially affecting the operation of the remaining electrodes.

Each cathode housing can be provided in any suitable structure, and may be formed from any suitable material, that can help fluidly isolate the catholyte from the anolyte while still allowing a desired level of ion transfer between the anolyte compartment and catholyte compartments while the apparatus is in use to achieve the desired reactions and metal formation (e.g. the housings can be substantially leak-tight). Optionally, at least a portion of the cathode housing may be provided by a suitable membrane material, such as a substantially rigid and porous ceramic membrane that can maintain separation between the anolyte and catholyte while allowing a desired degree of ion transfer. Optionally, the entire cathode housing or at least substantially the entire cathode housing may be formed from the porous ceramic membrane, and the membrane may be generally continuous such that is covers the front, rear, side and bottom faces of the cathode.

In the described embodiments the portions of the anodes and cathodes that are facing each other, and between which at least a majority of the electrolysis reactions are facilitated can be described as the respective active surfaces (e.g. the portions between which the electric potential is applied). Preferably, the active surfaces of the co-operating anode and cathode pairs can be substantially the same shape and size and can have substantially the same area and general geometric configuration. For example, the active surfaces of the anodes and cathodes can be selected so that a ratio of the areas anode active surface to an area of the cathode active surface is between about 0.5 and 2, and more preferably is between 0.8 to 1.2. In other words, the active surface of each cathode may be between about 50% and 200% of the active surface of the corresponding anode and is preferably between about 80% and 120%. More preferably, the active surfaces of the cathodes and anodes are substantially the same size.

Optionally, the cathode housing can also define a respective effective transfer portion that can be understood to be the portion of the housing that is disposed between the active surfaces or portions of a complimentary anode and cathode pair. The transfer portion of the housing can preferably include the porous membrane and can be sized so as to be generally the same size and shape as the transfer portions of the electrodes. For example, the transfer portion of the cathode housing may be sized such that the ratio of the housing transfer portion area and the area of the larger of the electrode transfer areas is between 0.5 and 2, and more preferably, such that it is between 0.8 to 1.2 relative to the largest electrode. Maintaining a housing active transfer area (e.g. where the membrane is located) ratio in the range of about 0.8-1.2 may help reduce the area open to carbonate ion transport, in contrast to the cells depicted in the prior art. That is, the size of the transfer portion of the porous membrane is preferably between 50% and 200% relative to the active surface of the larger of the associated electrodes (i.e., relative to the larger of the anode and cathode in an electrode pairing), and more preferably, is between 80% to 120% of that active surface.

Diffusion transport can be generally a function of active membrane area and may take place anywhere where a concentration gradient exists. By contrast, the desired ionic conduction in the described processes is largely limited to the area interposed between the cooperating anode and cathode—i.e. in the region between the transfer portions. Preferably, the active membrane area can be selected to generally match the desired transfer portion configuration and other portions of the cathode housing and/or membrane can be treated or configured to help limited ionic conduction in the non-transfer portion. This may help limit carbon and Li₂O accumulation resulting from transport of carbonate ions across other portions of the membrane and into the cathode compartment, which may be undesirable because it may reduce current efficiency and/or may cause elemental carbon sludge or oxide crust build-up in the catholyte. The apparatuses described herein may help reduce the negative effects of this phenomenon by closely matching the electrode and membrane area ratios as described, and/or by operating with relatively low-concentrations of dissolved Li₂CO₃ in the electrolyte bath (as discussed herein).

This may help reduce the area available for diffusion, and the driving force for the transport of carbonate ions across the porous membranes. That is, by limiting the active area to the ratios described herein, the ionic conduction may not be adversely materially affected, while carbonate ion diffusion transport from the membrane or other housing surfaces that are not substantially involved in ionic conduction may be reduced and may optionally be minimized or eliminated. This may help reduce the electrolytic production of carbon per unit of lithium produced, and thereby may help reduce the formation of the potentially harmful sludge, and reaction with the lithium metal to form insoluble lithium oxide. Reducing these unwanted reactions, may help reduce the operating cost of the described process and apparatus and may help extend the useful life of the membrane compartment, which may contribute to increased apparatus availability,

While for simplicity the apparatuses described herein are shown having their anodes submerged in a common anolyte bath and the cathodes enclosed by respective membranes to provide discrete cathode compartments other embodiments of the electrolyzer apparatus may have the opposite configuration. That is, other examples of the electrolyzer apparatus may be configured so that the two or more cathodes of the electrode assemblies are directly submerged in a common catholyte compartment and each anode may be enclosed within a suitable anode housing (such as a ceramic membrane) to provide a plurality of discrete anolyte compartments. This may be somewhat less preferable than the primary embodiments described herein, (for example it may require introducing feed material separately into each of the anolyte compartments and monitoring their individual parameters rather than being able to feed and monitor a common, larger anolyte bath) but could be utilized in some circumstances. That is, understood that the discussion of the configuration and operation of the cathodes and membranes is also applicable to embodiments in which the anodes are enclosed by the membranes.

Referring to FIG. 1 a, a schematic representation of features of one example of a molten salt membrane electrolyzer apparatus 2 is shown. The schematic drawings illustrate aspects of some features of the apparatus, and other elements of the apparatus (such as conduits, pumps, controllers and the like) have been omitted from this drawing for clarity/simplicity. Such components may be provided in some embodiments of the electrolyser apparatuses described herein.

Optionally, the electrolyzer apparatus 2 can be used for the production of lithium metal from lithium carbonate via an electrolysis process operating in a suppressed chlorine regime (described herein) and in a manner that may consume relatively less carbon per unit lithium produced than known apparatuses and processes.

The electrolyzer apparatus 2 in this example has a containment vessel 4 that is configured to define/provide a compartment for containing liquids, such as a molten salt, while the apparatus 2 is in use. The containment vessel 4 may have any suitable shape and size, based on the requirements for a given electrolyzer apparatus 2, and may have any suitable physical structure/arrangement that can provide a desired level of liquid containment. For example, the containment vessel may be generally rectangular or square in cross-sectional shape (i.e. when viewed from above), or may have rounded corners, be hexagonal, octagonal, cylindrical or the like. It may include a generally liquid impermeable bottom and side wall(s) and can be configured so that corresponding electrode assemblies can be submerged within the container liquid/molten salt.

The top of the electrolyzer apparatus 2 may be open (e.g. have an open top or upper end) as shown, or may at least be openable to help facilitate the positioning and optionally installation/extraction of the electrode assemblies, but may also tend to be generally covered and/or enclosed when the electrolyzer apparatus 2 is in use to help prevent the contents of the electrolyzer apparatus 2 from escaping and/or to help prevent unwanted foreign debris/objects from entering the electrolyzer apparatus 2. The electrolyzer apparatus 2 may also be sized to have an internal volume that can accommodate a desired amount of liquid, which in the case of the electrolyzers disclosed herein may be a molten salt, or the like.

In the example illustrated in FIG. 1 a, the containment vessel 4 has a generally rectangular cross-sectional shape and has a bottom wall 6 with an opposing upper end 14 and at least one side wall 8 that extends upwardly from the bottom wall 6 toward the upper end 14. Together, the bottom wall 6 and side wall 8 co-operate to generally provide the boundaries of an anolyte compartment 10 of the electrolyzer apparatus 2. In some embodiments, the containment vessel may have two, three, four, or more side walls.

In the illustrated example, the containment vessel 4 has an open upper end 14. In other embodiments, the upper end 14 may be partially or optionally fully enclosed with a fixed cover and/or may be reversibly or openably enclosed with a removable cover or roof. An upper wall is not shown in this schematic representation but may be included and positioned to help enclose the anolyte compartment 10 when the electrolyzer apparatus 2 is in use.

Optionally, the containment vessel 4 may be lined with a liner along at least a portion of its interior surface to help contain a molten salt and/or to help protect the bottom and side walls. The liner can be comprised of any suitable material that can withstand the expected operating conditions, including refractory bricks, castable cements, frozen salt or metal.

The containment vessel 4 may also optionally include a thermal insulating layer that surrounds at least a portion of the containment vessel 4 and can help reduce the transfer of heat of thermal energy between the anolyte compartment 10 and the surrounding environment. This may help reduce the amount of energy needed to keep the anolyte compartment at a desired operating temperature.

In this embodiment, the walls 6, 8 of the containment vessel 4 co-operate to at least partially define an anolyte compartment 10, that preferably has a generally open upper end that can be configured to receive the top-mounted (or at least top positioned, generally downwardly extending) electrode assemblies described herein. This can help facilitate the relatively easier installation and removal of the electrode assemblies (or at least portions thereof) into the anolyte compartment 10, as compared to arrangements in which the electrodes extend through the sidewalls or bottom wall of the containment vessel. For example, this may allow the anodes and/or cathodes to be removable from the anolyte compartment without having to drain the molten salt anolyte from the anolyte compartment.

As used herein, references to an open upper end are intended to describe structures which that have an open region toward their upper end through which an electrode assembly may be inserted in the anolyte compartment in a generally vertical manner, preferably without having to pass through the sidewall or bottom wall—and preferably from a mounting position that is not submerged within the anolyte while the apparatus is in use. This can help reduce the need to provide seals in the sidewall and bottom wall of the containment vessel, which may help reduce the chances of leakage and/or wear of the seal components. This does not however require that the upper end of the containment vessel 4 remain entirely “open” or unobstructed while the apparatus is in use. In fact, it may be preferable to generally cover and/or enclose the upper end of the electrolyzer apparatuses when they are in use (i.e. with the electrode assemblies already in place) for a variety of reasons (including, for example, operating efficiency and safety).

To help secure and mount the electrodes in their desired locations the apparatus 2 may include any suitable mounting apparatus, such as an anode mounting apparatus, a cathode mounting apparatus and the like. The mounting apparatuses may be the same or different for the anodes and cathodes, and optionally a single structural member—such as a beam, bracket or the like—may support at least one cathode and at least one anode and may therefore function as both an anode mounting apparatus and a cathode mounting apparatus.

The containment vessel 4 is designed to support the anolyte 12, any liner lining the containment vessel 4, and any other component that may be contained within or on or secured to the containment vessel 4 and may supply sufficient binding forces to help ensure leak-tightness of any lining and withstand the service temperatures without undue deformation. The containment vessel 4 may be formed from any suitable structural material, including but not limited to, steel, stainless steel, aluminum, or concrete. Optionally, the bottom wall 6 and side walls 8 of the containment vessel 4 may be reinforced with ribs or stiffeners to help provide the desired structural characteristics.

The anolyte compartment 10 is configured to contain a molten salt anolyte 12, that can include any suitable material for a given use of the electrolyzer apparatus 2. For example, the nature of the anolyte selected may vary depending on the type of feed material to be used and the corresponding type of metal that is to be produced. Some examples of suitable anolyte materials may include primarily chloride salts, such as lithium and/or potassium chlorides, bromide salts, such as lithium and potassium bromide, and iodide salts. such as lithium and potassium iodide.

If the electrolyzer apparatus 2 is to be configured to produce lithium metal, then one example of a suitable anolyte material is a salt that includes LiCl—KCl, preferably in a molar concentration ratio of between about 65:35 to 95:5 or to about 100:0, and that can be maintained at a temperature of between about 370-660° C. (which may be preferably at least about 10-100° C. higher than the melting point of the anolyte/electrolyte in some examples). In the illustrated example, the anolyte 12 comprises LiCl—KCl and the electrolyzer apparatus 2 is configured to utilize lithium carbonate (Li₂CO₃) as its feed material. Optionally, the feed material can be provided as needed while the apparatus is in use to maintain a desired composition, such as of between about 0.1-10% Li₂CO₃ wt, within the anolyte. Within this concentration and temperature range, the solubility of lithium carbonate within the anolyte may be sufficient to help scrub chlorine gas from the electrolyte when it is formed at the anode (as described herein), but not so high as to encourage unduly fast diffusion of carbonate ions into the cathode compartment at saturation.

When the electrolyzer apparatus 2 is in use, the anolyte material is heated and can be maintained at any suitable operating temperature that is sufficient to keep the anolyte in a sufficiently liquid state, while not being so hot to promote boiling or excessive evaporation of the electrolyte components, using any suitable heating apparatus. This can help facilitate the desired electrolysis reactions by helping to ensure that the anolyte, and feed material entrained therein, can circulate within the common anolyte bath within the apparatus 2 and between respective pairs of the anodes and cathodes. The specific operating temperature may vary based on the anolyte material, feed material and other factors. Preferably, when the electrolyzer apparatuses described herein are in use, the anolyte 12 may be maintained at an operating temperature that is between about 375° C. and about 750° C. degrees Celsius, between about 400° C. and about 725° C., and preferably may be between about 450° C. and about 700° C.

As illustrated in FIG. 1 a, the electrolyzer apparatus 2 has a first electrode assembly 16, which comprises a first anode 18, a first cathode housing 20, and a first cathode 30, and a second electrode assembly 32, which comprises a second anode 34, a second cathode housing 36, and a second cathode 46. In some embodiments, the electrolyzer apparatus comprises three, four, five, six, seven, eight, nine, ten or more electrode assemblies optionally arranged in an array, grid or the like (see FIGS. 3-10), while still being in fluid communication with the common anolyte bath, but only two electrode assemblies are shown in FIG. 1a for clarity.

In the illustrated example the first electrode assembly 16 and second electrode assembly are generally identical, but in other embodiments may be different. Descriptions of the operation of the first and second electrode assemblies 16 and 32 can be applicable to any electrode assemblies that may be provided in a given example of the electrolyser apparatus 2. In the illustrated example, the first anode 18 and second anode 34 both extend generally downwardly through the open upper end 14 of the containment vessel 4 into the common anolyte compartment 10. In such an arrangement, the first anode 18 and second anode 34 are preferably in fluid contact with the molten anolyte 12 contained in the common anolyte compartment 10.

To help define the multiple catholyte compartments within the common anolyte compartment 10, each cathode 30 and 46 is provided within a respective cathode housing 20 and 36. The cathode housings 20 and 36 are arranged to generally surround their respective cathodes 30 and 46 in a generally liquid-tight manner, and positioned so that the outer surfaces of the cathode housings 20 and 36 are also in fluid contact with the molten anolyte 14 in the common anolyte compartment 10.

In this arrangement the interior of each cathode housing 20 and 36 defines its respective first and second catholyte compartments 22 and 38, which contain respective molten salt catholyte material (identified using characters 24 and 40 respectively). While liquid separation between the anolyte and catholyte is preferably maintained while the apparatus 2 is in use, the anolyte and catholyte may optionally comprise the same or at least substantially the same materials. In this example the catholyte material also includes molten LiCl—KCl, in substantially the same ratios as the anolyte 14. Other catholyte materials may also be used.

In FIG. 1 a, the anodes 18 and 34 are shown in a side view and are understood to be generally planar members that extend into the page as shown. Another schematic representation of the first electrode assembly 16 is shown in FIG. 1b in which the anode 18 and 30 are illustrated as generally planar sheets, with the cathode housing 20 shown as a generally box-like structure formed from the suitable porous membrane material, the interior of which forms the first catholyte compartment 22. The locations of the anode 18, housing 20 and cathode 30 are exaggerated in FIG. 1b for illustrative purposes, and each of the pieces is intended to be positioned within the common anolyte bath. The front, active surface of the anode 18 faces the opposing face of corresponding cathode 30 and forms the anode active surface 48. The opposing active surface of the cathode 30 forms its reciprocal active surface 50. Preferably, the active surface of the anode 18 is configured and positioned to be substantially equidistant from the active surface of the cathode 30. If the electrodes 18 and 30 are substantially planar plates, this can be achieved by arranging the abode 18 so that it is parallel or at least substantially parallel to the cathode 30. Alternatively, the electrodes need not be parallel with each other to provide substantially equally spaced active surfaces. For example, the electrode surfaces may be concentric circular or cylindrical surfaces or other complimentary-shaped arcuate surfaces that are equally spaced from each other along their length/width.

Likewise, the second anode effective transfer area 52 is opposite and facing the second cathode effective transfer area 54. The portions of the membranes 28 and 44 that are disposed laterally between the opposing active surfaces 48 and 50, and 52 and 54 define the transfer portions 26 and 42 of the respective membranes 28 and 44.

The transfer portions 26 and 42 of the first and second porous membranes 28, 44 are preferably configured to permit the migration of lithium ions from the anolyte compartment 10 into the first and second catholyte compartments 22, 38, respectively, while resisting the migration of carbonate ions from the anolyte compartment 10. Restricting the transport of carbonate ions limits the rate of formation of undesirable cathode products, namely carbon and lithium oxide, which would otherwise reduce current efficiency through unwanted reaction 3 and may limit the life of the catholyte by contaminating it with carbon, and potentially reduce metal recovery by the formation of low-solubility lithium oxide through unwanted reaction 2. Relatively better cell performance may be achieved by minimizing the transport of carbonate ions from the anolyte to the catholyte.

In the illustrated example, the porous membranes 28, 44 help maintain a carbonate ion concentration gradient between the anolyte 12 and catholyte 24, 40 during electrolysis, such that the carbonate ion concentration in the catholyte 24, 40 is substantially lower than in the anolyte 12. Preferably, the concentration of carbonate ions within the catholyte is maintained between about 50 ppm and about 5000 ppm, and more preferably is less than about 100 ppm while the apparatus is in use.

The porous membranes 28, 44 may be formed of any suitable material that can substantially hinder carbonate ion diffusion transport from the anolyte compartment 10 into a catholyte compartment 22, 38. Preferably, the porous membrane is a non-wetting ceramic, such as alumina, magnesia, zirconia, lithium-aluminate, petalite, magnesium alumina spinal, mullite, or similar, and optionally may have a maximum pore size between 0.1-100 microns and an average pore size between 0.05-50 microns. More preferably, the porous membrane may have a maximum pore size of about 1 micron and average pore size less than about 0.5 microns. Further, the porous membrane preferably has an open porosity of between 10-80%, and more preferably between 30-60%. It is also preferred that the porous membrane is formed in one piece (e.g. of integral, one-piece construction) and is substantially free of joints as this may help prevent leakage.

In some embodiments, the cathode housings may be formed entirely from a porous membrane. In other embodiments, as illustrated in FIG. 1 a, a porous membrane may form only a portion, such as the transfer portions 26 and 42, of the cathode housings 20 and 36. Referring to FIG. 1 a, in this example the first cathode 30 is positioned within the first cathode housing 20 such that the first transfer portion 26 is disposed between the first anode 18 and the first cathode 30 and such that the first cathode 30 is in fluid contact with the catholyte 24 contained within the first catholyte compartment 22. Likewise, the second cathode 46 is positioned within the second cathode housing 36 such that the second transfer portion 42 is disposed between the second anode 34 and the second cathode 46 and such that the second cathode 46 is in fluid contact with the catholyte 40 contained within the second catholyte compartment 38.

If the cathode housings 20 and 36 were formed entirely from the porous membrane material it may be desirable to treat or otherwise modify some portions of the membrane to inhibit ion exchange through the membrane outside the desired transfer portions. For example, optionally, portions of the porous membrane and/or cathode housing may be treated outside of the transfer portions (whether there is a single transfer portion or multiple transfer portions on a given membrane, as discussed herein) to help inhibit the transmission of ions through regions of the cathode housing that are outside of the transfer portion. Optionally, portions of the membrane outside the transfer portion 26 or 42 may be treated to reduce their porosity and/or to inhibit ion transfer therethrough.

For example, a reduction of available ion transfer area outside the transfer portion may achieved by masking parts of the porous membrane (i.e. other than the transfer portions 26 and 42) using an appropriate coating or glaze, impregnating the porous membrane with a pore-filling substance, such as resin or fine particles, or selectively slip-casting parts using different green material formulations. Alternatively, or in addition, the transport of carbonate ions through the membrane material may be reduced and/or substantially eliminated by at least superficially infiltrating the porous membrane with an ion-selective material, such as a super-ionic conductor, such as Li β-Al₂O₃, Li₅AlO₄, Li₂S—P₂S₅, or similar super-ionic conductors which are stable at high temperatures. Super-ionic conductors can have effective conductivity of about 10-1000× lower than molten salt electrolytes described herein, and accordingly if such materials are applied to the transfer portions 26 and 42, they would be applied in relatively thin layers so as to limit resistive losses between the electrodes. Such treatment layers may be between about 0.01 microns and about 100 microns thick. By at least partially infiltrating the pores of the porous membranes in the transfer portions 26 and 42, the super-ionic material can be surrounded by the porous membrane matrix, which can help provide mechanical support for the coating material. This may help enable the use of acceptably thin layers to be formed inside the first few pores on the outer surface of the membrane while providing sufficient durability. The super-ionic conductor thickness can be controlled using any suitable technique, including by applying a viscous glaze of super-ionic conductor material and, if necessary, grinding or otherwise machining the outer layer of the porous membrane until the desired thickness of super-ionic conductor material remains.

By helping to limit the rate of carbonate ion transport through the use of porous membranes with sub-micron average pore size, closely matched in active surface to the electrodes, and optionally infiltrated with super-ionic conductor material, the rate of production of unwanted products can be substantially reduced. Such a reduction can increase the current efficiency and extend the time between catholyte and porous membrane replacement.

Optionally, the anodes and cathodes can be any suitable shape. In the illustrated example, the anodes 18, 34 have the shape of a generally planar plate that is substantially parallel to the respective cathodes 30, 46, which also have the shape of a generally planar plate.

Optionally, some or all of the electrodes (including the anodes, cathodes or both) may be removable from the containment vessel 4. For example, the anodes 18 and 34 can be removable from the anolyte compartment to help facilitate inspection, maintenance and/or replacement of each given anode. In the illustrated example, the anodes 18 and 34 (and/or cathodes 30 and 46) can be removed in the generally upward direction, by lifting them out of the anolyte bath. Preferably, at least some of the anodes 18 and 34 and/or cathodes 30 and 46 can be removed independently of other ones of the cathode housings, cathodes, and other anodes. This can help facilitate the repair of one electrode without requiring removal of other electrodes. Optionally, at least some of the electrodes can be removable without having to drain the anolyte 12 from the anolyte compartment 10. This allows for the electrodes to be replaced (for example, when worn), without requiring the disassembly of the containment vessel 4.

The electrolyzer apparatus 2 is preferably operated at a relatively high current density of at least 0.75 A/cm² on either electrode in an electrode assembly on either the anode or cathode), and more preferably 1 to 2 A/cm² or more. In other examples, the current density can be between about 0.75 or 1 A/cm² and about 4 A/cm², and preferably is at least 1.2 A/cm² so that electrolysis of both lithium chloride and lithium carbonate can be achieved in accordance with the various reactions described herein. The relatively high current density operation of the electrolyzer apparatus 2 can help achieve a relatively high specific productivity, which may help reduce the capital and/or operating casts for a given production capacity. For example, the specific productivity for the illustrated apparatus may be between about 3 kg Li/m² electrolyte bath surface/hr and about 15 kg Li/m² electrolyte bath surface/hr, and optionally may be about 5-7.5 kg Li/m² electrolyte bath surface/hr.

In some embodiments, the anodes (e.g. 18 and 34) may be made of any suitable carbon-based material including, for example, blocks of graphite, semi-graphite, vitreous carbon, or another carbonaceous material. When the electrolyzer apparatus 2 is in operation, carbonate ions may be oxidized at the anodes according to one or more of reaction 4, 5, and 6, which may contribute to the consumption of the anode material.

Li₂CO₃(s, l)+1/2C(s)=2Li(l)+3/2CO₂(g); E ^(o)=−2.127 V   [4]

Li₂CO₃(s, l)+C(s)=2Li(l)+CO_(2(g))+CO_((g)) ; E ^(o)=−2.226 V   [5]

Li₂CO₃(s, l)+2C(s)=2Li(l)+3CO_((g)) ; E ^(o)=−2.434 V   [6]

While not wishing to be bound by any particular theory or mode of action, under normal operating conditions, it is expected that anodes will last several days to several weeks, after which they will need to be replaced. The self-contained unitary construction and top-mounted configuration in the illustrated example allows for removal of the anodes using an overhead bridge crane or other lifting device, optionally without needing to shut the cell down for prolonged periods of time. This arrangement thus may not only help reduce downtime but the life of the electrolyzer apparatus 2 may not be limited by the life of the anodes, which may help reduce and/or eliminate the costs associated with rebuilding the electrolyzer apparatus 2, and/or the opportunity cost of ceasing operations for maintenance.

In other embodiments, the anodes may comprise a metal, ceramic, cermet, or composite material that are generally inert or optionally at least semi-inert to the electrolytic process and the product gases. Such materials can include metals, ceramics, cermets, composites, and are characterized in having very low rates of consumption during electrolysis. These inert or semi-inert anodes may reduce the need for removal and replacement of the anodes, thereby reducing the maintenance effort required to operate the plant, and thus may reduce both the number of personnel and facilities needed for a given throughput. By using inert or semi-inert anodes, the electrode spacing and/or gap between the anode and cathode may be maintained at a substantially constant (subject to less than about 5% change while in use) and preferably relatively small value (in the range of 0-1%), which may help reduce the resistive heating losses incurred in the electrolyzer. Additionally, using an inert or semi-inert anode may help reduce carbon dioxide emissions per unit of lithium metal produced, by forcing the reaction within the apparatus 2 to the less carbon-intensive variant in reaction 7.

For example, electrolytic reactions 4, 5 and 6 can produce CO and CO₂, while reaction 7 can produce O₂ and CO₂. These gases can evolve at the anode surface (i.e. at the surface of anode 18 or 34), float to the surface of the anolyte 14, and can then be captured by the gas and conducted away from the cell, for example via a suitable gas extraction apparatus (not shown in FIG. 1, but that may contain a gas capture hood connected to a suitable gas removal conduit).

Li₂CO₃(s, l)+1/2C(s)=2Li(l)+3/2CO₂(g); E ^(o)=−2.127 V   [4]

Li₂CO₃(s, l)+C(s)=2Li(l)+CO_(2(g))+CO_((g)) ; E ^(o)=−2.226 V   [5]

Li₂CO₃(s, l)+2C(s)=2Li(l)+3CO_((g)) ; E ^(o)=−2.434 V   [6]

Li₂CO₃(s, l)=2Li(l)+CO₂(g)+1/2O₂ ; E ^(o)=−3.145 V   [7]

A suitable power supply can also be provided to apply an electric potential between respective pairs of electrodes. Preferably, the power supply is relatively oversized as compared to known apparatuses for merely completing electrolysis of Li₂CO₃ and can be configured to provide a relatively high overpotential between the electrodes. As used herein, overpotential can be used to refer to an arrangement in which the electric potential applied between pairs of electrodes is purposefully higher, and preferably is substantially higher, than the electric potential that is required to complete the electrolysis of the lithium carbonate feed stock material. In contrast to conventional systems that are configured to reduce/minimize power consumption, for example by operating with the lowest electric potential that is sufficient to process the given feed stock, the processes and apparatuses described herein can be intentionally operated at a seemingly less efficient electric overpotential because it has been discovered that the overpotential can provide other advantages for the overall process/apparatus—such as driving other reactions arid helping to control reaction by products and off gases.

That is, the electric potential that is applied between the electrodes can be between at least 1.5V greater than the electric potential that is required to merely complete electrolysis of Li₂CO₃ so that other materials and optionally may be between about 1.5-20V greater than the electric potential that is required to merely complete electrolysis of the Li₂CO₃feed stock, such as LiCl may also be subject to electrolysis. While the amount of electrical potential may vary in a given apparatus, it is preferably is substantially greater than the equilibrium potential of lithium chloride so that it is sufficient to i) initiate electrolysis of lithium carbonate and ii) be greater than the electric potential required to initiate LiCl electrolysis. For example. the electrical potential may be at least about 4 V, and is preferably at least 7V. In some embodiments, the electrical potential may be between about 7V and about 12V, and optionally may be at least 15 V. In the illustrated example, the electrolyzer apparatus 2 has a power supply 56, which is configured to apply an electrical potential between the first anode 18 and first cathode 30 and can also provide power to any of the other electrode pairs within the apparatus 2. The power supply can be any suitable type of power supply.

It is believed that at least partially as a consequence of the simultaneous occurrence of these anode reactions, Cl₂, CO₂ and CO gasses are evolved at the surface of the anodes 18 and 34. The inventors have discovered that relatively small concentrations of Li₂CO₃ react readily with Cl₂ as it bubbles up through the anolyte 14, converting it to LiCl, CO₂ and O₂ according to reaction 8. This can, in effect, act as an inherent chlorine scrubber. Under these conditions, the inventors have discovered that there is a near-total suppression of Cl₂ emission from the apparatus 2, even at high-over potential and anode current densities.

Li₂CO_(3(l))+Cl_(2(g))=2LiCl_((l))+CO₂(g)+1/2O_(2(g))   [8]

The apparatuses described herein can utilize this effect to bias the production of lithium metal to towards reactions 1 and 7 at the expense of reactions 4, 5 and 6. By doing so, the quantity of carbon required per unit of metal may be reduced from the stochiometric ˜0.5 kg C/kg Li to about 0.4 C/kg Li or less, or about 0.3 kg C/kg Li or less. To the extent that carbon for the reactions is consumed from the anodes 18 and 34, etc. this reduction in carbon consumption may be advantageous, as it may help reduce the frequency of anode changes and may help reduce the operating costs of the systems.

While it is generally desirable to avoid the creation/release of chlorine from electrolysis reactors as noted herein, the inventors have discovered that the conditions enabled by the use of the electrolyzer apparatuses described herein may be advantageous enough that in some circumstances it may actually justify the introduction of additional chlorine gas into the apparatus while it is in use. It has been discovered that the introduced chlorine may be largely consumed as described and, while not wishing to be bound by any particular theory or mode of action, the introduction of chlorine gas within the catholyte compartments 22 and 38 may surprisingly help inhibit carbon and/or lithium oxide fouling of the cathode, by reacting with the Li₂CO₃ present within the catholyte to produce LiCl and carbon dioxide. The LiCl may be subsequently electrolyzed under the overpotential operating conditions, which may help improve apparatus efficiency and/or lithium production as compared to operating the apparatus in the absence of the added chlorine gas. The introduction of chlorine gas in this manner may also help inhibit damage to the porous membranes by reacting with excess lithium that may be present in the catholyte compartment.

Additionally, chlorine gas may be introduced into the anolyte, in conjunction with excess Li₂CO₃ to convert the latter to LiCl. This is advantageous, as it allows LiCl lost from the electrolyte to evaporation to be replaced without resorting to purchases of the relatively more costly LiCl, and thereby reducing the operating cost of the plant, and simplifying the plant supply chain.

Accordingly, the electrolyzer apparatus may include a chlorine delivery system that is configured and operable to introduce chlorine gas into at least some of the catholyte or anolyte compartments while the apparatus is in use. The chlorine delivery system may include any suitable hardware and gas conveying components, including conduits, hoses, pipes, spargers, bubblers, valves, pumps/compressors, filters and the like that are configured to transport gas from the chlorine gas source (e.g. a gas tank or other gas supply) and introduce it within the catholyte compartments.

Optionally, instead of being arranged so that each cathode only engages a single anode (and vice versa) as shown in FIG. 1 a, an electrolyzer apparatus can be arranged with multiple electrodes closely-spaced together and so that a given cathode may be positioned with and engage two anodes (and vice versa). In such arrangements, each cathode housing may be configured to provide two transfer portions on opposing sides of the cathode, each registered with the active surface of the opposing anode.

The apparatuses described herein may be used in a process for producing lithium metal from lithium carbonate, and preferably for producing relatively high-purity lithium metal from lithium carbonate using a membrane electrolysis process operating in the suppressed chlorine regime (SCR). To achieve SCR operation the apparatus described herein can be operated so that the desired, applied overpotential and lithium carbonate concentration are maintained within the desired ranges while the apparatus is in use, while also reducing and/or minimizing the diffusion of carbonate ions into the cathode compartments, and the consumption of carbon at the anode.

In one preferred example, both the anolyte and catholyte is a LiCL-KCl melt, with a molar concentration ratio of 65:35 to 95:5, maintained at 475-660° C. Advantageously, within this concentration and temperature range, the solubility of lithium carbonate is sufficient to scrub chlorine gas from the melt when it is formed at the anode, but not so high as to encourage unduly fast diffusion of carbonate ions into the cathode compartment at saturation.

Electrolysis is carried out with a potential at least 1-1.5V, or more in excess of that required for lithium carbonate electrolysis; in other words with potential sufficient or greater than that required for lithium chloride electrolysis. Under these conditions, lithium metal may be electrolytically produced according to reactions 1, 4, 5, 6, 7. Contrary to conventional apparatuses, no attempt is made to operate in the low-voltage operating regime to realize energy savings, as this would result in undesired, relatively low current densities for practical cell configurations. Instead, energy consumption may be reduced by operating with a lithium chloride-rich electrolyte.

Within the electrolyte concentration range specified, electrical conductance of the electrolyte may be 15%-200% higher than the eutectic 60:40 melt of the conventional processes, which may lead to reduced resistive heat losses. The addition of lithium carbonate may have a further effect in enhancing electrical conductance, thereby further reducing the energy consumption.

Counterintuitively, this mode of operation does not result in the production of material amounts of chlorine gas, and its many associated drawbacks. While chlorine gas is temporarily produced at the anode, the presence of significant quantities of lithium carbonate in the melt adjacent to the anode may cause scrubbing of the chlorine gas, and conversion of the lithium carbonate into lithium chloride according to reaction 8.

Advantageously, operation according to the present teachings may help allow lithium to be produced from carbonate with substantially reduced carbon consumption, because reactions 1 and 7 do not rely on carbon from the anode. As a result, by establishing electrolytic conditions favorable to these reactions, the anode carbon consumption per kilogram of metal produced can be substantially reduced.

Table 1 shows experimental results which indicate the reduction, as compared to one representative example of a process known in the art.

Another advantage of the present teachings may be that, unlike the prior art, the present invention need not be limited in the current density that can practically be achieved, because electrolysis potentials significantly in excess of that theoretically required for electrolysis of carbonate can be applied. For example, current densities in excess of 1 A/cm² can be maintained according to the present teachings, while those of the representative, conventional apparatus were limited to 0.25-0.5 A/cm².

Operation at current densities in excess of 1 A/cm² helps reduce the specific flux of carbonate ions across the porous membrane per kilogram of metal produced, thereby resulting in reduced relative production of undesirable elemental carbon sludge in the catholyte compartment.

According to an aspect of the present teachings, SCR operation can be practically maintained by monitoring the anode gas to determine if the concentration of chlorine gas exceeds a monitoring threshold—e.g. if an amount of chlorine gas is present in the anode gas which would otherwise be substantially chlorine free. Chlorine gas breakthrough (detection of chlorine gas in the anode gas) signals that the lithium carbonate concentration in the anolyte bath has fallen below the target level needed for effective scrubbing and therefore lithium carbonate should be added to the anolyte. Chlorine breakthrough can occurs when the dissolved lithium carbonate concentration within the anolyte falls below about 0.1-0.5 mol %. Accordingly, the apparatuses described herein may be operated with a dissolved lithium carbonate concentration that is at least 0.1 mol %, 0.2 mol %, 0.3 mol %, 0.4 mol %, 0.5 mol %, 0.6 mol %, 0.7 mol %, 0.8 mol %, 0.9 mol %, 1 mol % or greater.

According to the present teachings, conditions favouring low anode carbon consumption can be maintained by monitoring the CO2/O2 ratio in the off-gas collected from the anolyte compartment and keeping this in the range 2-2.5. This can be done, for example, by adjusting the rate of lithium carbonate feed, adjusting the current density or maintaining an excess inventory of lithium carbonate in the anolyte and controlling the electrolyte temperature to maintain the desired saturation concentration of dissolved lithium carbonate. For example, by raising the temperature, additional lithium carbonate can be forced to dissolve into the anolyte from an inventory of solid precipitate maintained on the bottom of the electrolyzer.

TABLE 1 Process According to the Prior Art vs. the Present Invention Process Conditions According to one the Process Conditions teachings of a According to one conventional process Example of the Present (Kruesi) Teachings Electrode 3-5 V 7-12 V Potential Current Density 0.07-0.33 A/cm² 1.0-2.0 A/cm² Carbon 0.65 kg C/kg Li 0.25-0.5 kg C/kg Li Consumption Electrolyte LiCl-KCl Eutectic LiCl-KCl (60:40 molar) 65:35 to 95:5 molar CO₃ ²⁻ Conc. 0.75-5 mol % 0.35-0.75 mol % Operating 522° C.-722° C. 475° C.-650° C. Temperature

Referring to FIG. 2, a schematic illustration of another example an electrolyzer apparatus 1002 is illustrated. The Apparatus 1002 is generally analogous to electrolyzer apparatus 2, and analogous features are identified using like reference characters indexed by 1000. In this apparatus 1002, the electrodes are closely spaced together such that an electric potential is applied on both sides of some of the electrodes.

In this apparatus 1002, the second electrode assembly 1032 is adjacent the first electrode assembly 1016 such that the first cathode 1030 is disposed between and is optionally equally spaced between the first anode 1018 and the second anode 1034 so as to enable an electric potential to be applied across both gaps. Arranging the electrodes in this manner may help reduce the overall size of the apparatus 1002. In such an arrangement, the first cathode housing 1020 comprises a first transfer portion 1026 disposed between and registered with the active surfaces 1048 and 1050, and a second transfer portion 1058 disposed between and registered with the active surface 1062 on the opposite side of the cathode 1030 and the active surface 1064 on adjacent anode 1034. This second transfer portion 1058 includes an additional porous membrane region, which permits migration of lithium ions but resists the migration of carbonate ions from the anolyte compartment 1010 into the first catholyte compartment 1022.

FIGS. 3-10 illustrate an alternative embodiment of an electrolyzer apparatus 2002 that is generally analogous to electrolyzer apparatus 2, and in which analogous features are identified using like reference characters indexed by 2000.

In this embodiment, the containment vessel 2004 is generally square in cross-sectional shape, and has a bottom wall 2006 with an opposing upper end 2014 (FIG. 6) and at least one side wall 2008 that extends upwardly from the bottom wall 2006 toward the upper end 2014. Together, the bottom wail 2006 and side wall 2008 co-operate to generally provide the boundaries of an anolyte compartment 2010 of the electrolyzer apparatus 2002. In this embodiment, the electrode assemblies, including assemblies 2016 and 2032 (FIG. 10) are closely spaced and arranged so that the anodes (e.g. 2018 and 2034) and cathodes (e.g. 2030 and 2046) are alternatingly arranged in two rows (see also FIG. 5a ).

To help define the multiple catholyte compartments within the common anolyte compartment 2010, each cathode 2030 and 2046 is provided within a respective cathode housing 2020 and 2036. The cathode housings 2020 and 2036 are arranged to generally surround their respective cathodes 2030 and 2046 in a generally liquid-tight manner, and positioned so that the outer surfaces of the cathode housings 2020 and 2036 are also in fluid contact with the molten anolyte in the common anolyte compartment.

In this arrangement the interior of each cathode housing 2020 and 2036 defines its respective first and second catholyte compartments 2022 and 2038, which contain respective molten salt catholyte material. While liquid separation between the anolyte and catholyte is preferably maintained while the apparatus 2002 is in use, the anolyte and catholyte may optionally comprise the same or at least substantially the same materials. In this example the catholyte material also includes molten LiCl—KCl, in substantially the same ratios as the anolyte. Other catholyte materials may also be used.

In FIG. 10, the anodes 2018 and 2034 are shown in a side view and are understood to be generally planar members that extend into the page as shown. The front face of the anode 2018 faces the opposing face of corresponding cathode 2030 and forms the anode active surface 2048. The opposing surface of the cathode 2030 forms its reciprocal active surface 2050. Likewise, the second anode effective transfer area 2052 is opposite and facing the second cathode effective transfer area 2054. The portions of the membranes 2028 and 2044 that are disposed laterally between the opposing active surfaces 2048 and 2050, and 2052 and 2054 define the transfer portions of the respective membranes 2028 and 2044.

The transfer portions 2026 and 2042 of the first and second porous membranes 2028, 2044 are preferably configured to permit the migration of lithium ions from the anolyte compartment 2010 into the first and second catholyte compartments 2022, 2038, respectively, while resisting the migration of carbonate ions from the anolyte compartment 2010. Restricting the transport of carbonate ions limits the rate of formation of undesirable cathode products, namely carbon and lithium oxide, which would otherwise reduce current efficiency through unwanted reaction 3 and may limit the life of the catholyte by contaminating it with carbon, and potentially reduce metal recovery by the formation of low-solubility lithium oxide through unwanted reaction 2. Relatively better cell performance may be achieved by minimizing the transport of carbonate ions from the anolyte to the catholyte.

In the illustrated example, the porous membranes 2028, 2044 help maintain a carbonate ion concentration gradient between the anolyte and catholyte during electrolysis, such that the carbonate ion concentration in the catholyte is substantially lower than in the anolyte. Preferably, the concentration of carbonate ions within the catholyte is maintained between about 50 ppm and about 5000 ppm, and more preferably is less than about 100 ppm while the apparatus is in use.

In this embodiment, the electrodes are removable from the containment vessel 2004 and the apparatus 2002 includes an anode mounting apparatus 2006 from which an anode (e.g. 2018) can be suspended and extend downwardly into the anolyte compartment 2014. In the illustrated example (see also FIG. 3), the anode mounting apparatus 2066 includes an elongate anode mounting beam that extends over the upper end 2014 of the containment vessel 2004 and the first anode 2018 is suspended from the beam. Another anode is also supported by the same beam. Preferably, the anode mounting apparatus 2066 is detachable and removable from the containment vessel 2004 which can facilitate access to the anodes mounted thereon. Optionally, some or all of the anodes may be detachable from the mounting beam. optionally via the use of an intermediary anode mounting stub 2090 (FIG. 8), so that the anode 2018 may be detachable from the anode mounting apparatus 2066, which allows the first anode 2018 to be removed from the anolyte compartment 2010 and separated from the mounting beam and replaced with a new anode. Optionally, the anodes mounted to a common mounting beam may be individually detachable from the beam.

Similarly (see FIGS. 9a and 9b ), the electrolyzer apparatus 2002 may have a cathode mounting apparatus 2078 from which one or more cathodes and optionally the associated cathode housings can be suspended and extend downwardly into the anolyte compartment 2010. In the illustrated example, the cathode mounting apparatus 2078 includes an elongate beam that is generally similar to the beam used in the anode mounting apparatus 2066 and that extends over the upper end 2014 of the containment vessel 2004 and the first cathode 2030 is suspended from the cathode mounting apparatus 2078. Preferably, the cathode mounting apparatus 2078 is detachable from the containment vessel 2004, which allows the cathode secured to the cathode mounting apparatus 2078 to be removed from the anolyte compartment 2010 with the cathode mounting apparatus 2078. Optionally, a cathode housing, may also be suspended from the cathode mounting apparatus 2078, such that when the cathode mounting apparatus 2078 is removed from the anolyte compartment 2010, the cathode and its associated cathode housing is removed. Optionally, the cathode housing may be connected to the beam of other support apparatus directly or alternatively, as illustrated in this example the cathode housing 2020 may be at least partially connected to and supported by the cathode 2030 itself. Optionally, the cathodes mounted to a common mounting beam may be individually detachable from the beam.

In some embodiments, such as the illustrated example, the electrolyzer apparatus 2002 may have a plurality of anode mounting apparatuses 2066 and cathode mounting apparatuses 2078 in an alternating arrangement. Preferably, each electrode mounting apparatus spans or partially spans the electrolyzer apparatus 2002 transversely across the longitudinal axis. More preferably, the adjacent anode mounting apparatuses 2066 and cathode mounting apparatuses 2078, optionally in combination with the use of roof panels and other such members, may cooperate to cover all of or substantially all of the upper end 2014 of the containment vessel 2004 (for example, see FIG. 5a ) when the apparatus 2002 is in use. The anode and cathode mounting apparatuses may be configured in any suitable manner, including but not limited to being supported by the containment vessel 2004, being suspended from an external structure (walls or roof of an enclosing structure/building), or one type of electrode mounting apparatus may support the other.

Having a plurality of closely-interleaved top-mounted electrode mounting apparatuses, may help the present electrolyzer apparatus 2002 have a relatively larger electrode area within a given overall apparatus footprint and anode-to-cathode spacing. This may help reduce the overall size of the electrolyzer apparatus, which may help facilitate its use in locations that could not easily accommodate conventional apparatuses and may help reduce the overall cost of a plant of given production capacity.

Such a repeating electrode configuration may also may help enable a relatively large number of electrode pairs to be installed in parallel within the single electrolyzer apparatus 2002 (and preferably with the anodes being directly submerged in a common molten salt, anolyte bath in the common anolyte chamber 2010), thereby allowing relatively higher capacity production in the common vessel 2004 of an electrolyzer apparatus 2002 (e.g. while only having to provide and maintain a single anolyte bath).

Optionally, the anode mounting apparatuses 2066 and cathode mounting apparatuses 2078 may also incorporate other functional components of the apparatus 2002, including aspects of the power connection/supply systems, electrolyte supply, chlorine gas supply, feed material supply, lithium metal extraction and other such apparatuses. Incorporating these subsystems into the structures forming the anode mounting apparatuses 2066 and cathode mounting apparatuses 2078 may help simplify the design and construction of the vessel 2004 and/or may help facilitate access to such sub-systems while the apparatus 2002 is in use (for example, when the anode mounting apparatuses 2066 and cathode mounting apparatuses 2078 are removed from the vessel 2004). This may also help reduce the number of separate ancillary systems (electrical bus components, feed systems, gas supply and off-gas systems, tapping system, control systems, instruments, etc.) that are needed for a given metal production capacity, thereby reducing the capital expenses required to set-up the present electrolyzer apparatus 2002, as compared to known electrolyzer configurations.

This integration of apparatus 2002 subsystems may also help make it relatively easier to operate the described electrolyzer apparatus 2002. For example, as each of the anode mounting apparatuses 2066 and cathode mounting apparatuses 2078 span across a common anolyte bath the feed material supply apparatus integrated into any one of the anodes mounting apparatuses 2066 and cathode mounting apparatuses 2078 may be used to supply feed material to multiple electrode pairs. That is, because the operator need not maintain the balanced of feed material or other components in multiple, discrete anolyte compartments a common feed may support the operation of multiple electrode pairs. Instead, the use of a common anolyte compartment 2010 into which at least two or more pairs of electrodes can be submerged may help ensure that each anode is exposed to an anolyte having the same, and preferably the desired, composition as the present electrolyzer apparatus 2002 is in use. For example, feed material that is introduced in one region of the containment vessel may circulate within the anolyte and may be available for reaction at a plurality of different electrode assemblies in the examples of the electrolyzer apparatuses described herein.

In some embodiments, the one or more anode mounting apparatuses are configured to be self-contained units or substantially self-contained units. The anode mounting apparatus 2066 in the illustrated example comprises an anode structural member 2088 (i.e. a beam in this example). Looking to FIGS. 8a and 8b , the illustrated anode mounting apparatus 2066 also comprises an anode electrical connector 2068 (e.g. a bus connection) that provides electrical communication between the anodes and the power source, anode stubs 2090 for helping to attach the anodes, the first anode 2018, an anode gas extraction apparatus 2072 (including a gas capture hood 2074 in communication with the anode gas removal conduit 2076—FIG. 5b ), and insulating roof lining elements 2092, each of which are directly or indirectly affixed to the anode structural member 2088 (see FIG. 8).

The anode structural member or members 2088 and anode stubs 2090 may be made of any suitable material, such as steel, stainless steel, or other conductive structural materials capable of withstanding the process temperature.

In the illustrated example, the anode electrical connector 2068 electrically connects the first anode 2018 to the power supply 2056 when the anode mounting apparatus 2066 is attached to the containment vessel 2004. When the anode mounting apparatus 2066 is detached from the containment vessel 2004, the electrical connection between the first anode 2018 and the power supply is interrupted. Optionally, the anode mounting apparatus 2066 may have an insulating lining (e.g. roofing elements 2092) disposed between the anolyte compartment 2010 and the anode electrical connector 2068 to inhibit heat transfer from the anolyte to the anode electrical connector 2068 when the electrolyzer apparatus 2002 is in use. The insulating lining may be removable with the anode mounting apparatus 2066.

The anode electrical connector 2068 may be made of any suitable conductive material with low electrical resistance, such as copper, brass, aluminum, silver, bronze, steel or iron, to help reduce, and optionally minimize the electrical resistive losses and heating of the structure. Preferably, anode electrical connectors 2068 are connected to the anode stubs 2090 via a low electrical resistance method, such as welding, brazing, riveting, or bolting.

In some embodiments, the anode mounting apparatus can include at least some components of a gas extraction apparatus that can be used to remove product gases as they accumulate in the head space toward the upper end 2014 of the vessel 2004 when it is in use. In the illustrated example, the gas extraction apparatus 2072 comprises a gas capture hood 2074 configured to capture product gases formed adjacent an anode and bubbling out of the anolyte. The gas capture hood 2074 is positioned above the first anode 2018. The gas extraction apparatus 2072 may also include a gas removal conduit 2076. In the illustrated example, the gas removal conduit 2076 extends from the gas capture hood 2074 and is configured convey the product gases away from the containment vessel 2010.

In the illustrated example, the gas capture hood 2074 is a gas-tight sheet metal hood, isolated electrically from the anodes via the anode roof lining elements 2092 (see FIG. 10). The bottom lip of each gas capture hood 2074 is immersed below the minimum level of the electrolyte bath. Preferably, the gas capture hoods 2074 are sized so that their width spans substantially the entire space between the porous membranes 2028, 2044 on adjacent cathode housings (see also FIG. 10). This arrangement can capture a substantial portion of the gas that is evolved at the anode and, because of the immersion, can generate sufficient pressure to drive the gas out of the gas removal conduit 2076 and into a gas cleaning system (not shown). Such close capture of the gas may allow it to be used as a process input, a by-product stream, or directed to carbon sequestration, all of which may reduce the carbon footprint of the process.

In other embodiments, the gas capture hood 2074 may be formed directly into the anode roof lining elements 2092, defined by the adjacent cathode mounting apparatus roof lining elements (discussed below), or omitted entirely, with anode gas captured by the gas space 2094 defined by the anode and cathode mounting apparatuses 2066, 2078, containment vessel 2004, and anolyte.

Preferably, at least a portion of the gas extraction apparatus 2072 is removable from the containment vessel 2004, optionally with the anode mounting apparatus 2066. It is also preferable that the gas capture hood 2074 is electrically isolated from the anode secured to the anode mounting apparatus 2066.

The gas capture hood 2074 and gas removal conduit 2076 may be made of stainless steel or any other suitable material that is capable of withstanding prolonged exposure to chloride immersion and chloride mist under high temperature, as well as compatible with constant exposure to high-temperature carbon dioxide gas, and occasional contact with chlorine gas.

The anode roof lining elements 2092 may be of sufficient strength to remain attached to the anode mounting apparatus 2066 during handling, and be compatible with chloride melts, while also providing sufficient thermal insulation to protect the anode structural member 2088 from excessive temperatures. Suitable materials may include fireclay bricks and castables, alumina bricks and castables, calcium silicate board, alumina silicate board, and other similar refractory materials known to those skilled in the art.

In some embodiments, the one or more cathode mounting apparatuses are configured to be self-contained units or substantially self-contained units. The cathode mounting apparatus 2078 in the illustrated example comprises a cathode structural member 2096. Looking to FIGS. 9a and 9b , the illustrated cathode mounting apparatus 2078 also comprises a cathode electrical connector 2084, cathode stubs 2098, the first cathode 2030, gas capture elements (which in this example are the porous membranes 2028, 2044), shielding gas conduits 2100 (which can include any required valves, conduits and the like and can be connectable to be a suitable source of an inert shield/cover gas), a lithium metal extraction assembly 2080, a lithium metal extraction conduit 2082, and cathode roof lining elements 2102, each of which are directly or indirectly affixed to the cathode structural member 2096.

It may be desirable to remove and replace inoperable porous membranes or other aspects of the cathode housing when the apparatus 2002 is in use or has been used. For example, even selective porous membranes may permit some quantity of carbonate ions to diffuse into the catholyte chamber. These carbonate ions may react either with the lithium metal, or through direct electrolysis, produce insoluble elemental carbon and lithium oxide according to reaction 2 or 3 described herein. Over time, the carbon can build up as a sludge, at least some of which may accumulate within the porous membranes in the cathode housings, eventually rendering the membranes and electrode less effective and potentially inoperable. As a result, it may be desirable to service and/or replace the porous membranes and catholyte periodically over the life of the apparatus 2002. Affixing the porous membranes to the cathode mounting apparatus 2078 (and optionally to the cathodes themselves), may help facilitate that relatively easy removal and replacement of selected porous membranes by removing the cathode mounting apparatus 2078 as a unit, optionally using an overhead bridge crane or other lifting device, without needing to shut the apparatus 2002 down for prolonged periods of time. This arrangement may help reduce downtime and the life of the electrolyzer 2002 may not be limited by the build-up of elemental carbon sludge or lithium oxide in the porous membrane or cathode compartment.

The cathode structural member 2096, cathode stubs 2098, and cathode roof lining element 2102 are analogous to similar components of the anode mounting apparatus 2066, as described herein.

In the illustrated example, the cathode mounting apparatus 2078 has a cathode electrical connector 2084 that electrically connects the first cathode 2030 to the power supply 2056 when the cathode mounting apparatus 2078 is attached to the containment vessel 2004. When the cathode mounting apparatus 2078 is detached from the containment vessel 2004, the electrical connection between the first cathode 2030 and the power supply is interrupted.

The cathode mounting apparatus 2078 may have a lithium metal extraction assembly 2080 to extract lithium metal that collects in the catholyte. In the illustrated example, the lithium extraction assembly 2080 includes a lithium extraction conduit 2082 that extends from an upper end proximate the cathode mounting apparatus 2078 to a lower end that is disposed within the first catholyte compartment 2022. Optionally, the lithium extraction conduit 2082 is removable from the containment vessel 2004 with the cathode mounting apparatus 2078.

In some embodiments, electrolyzed metal can accumulate directly in the catholyte compartments. A vacuum can be applied continuously or intermittently to each lithium extraction assembly 2080 to withdraw metal as it is formed. The vacuum draws metal up the lithium extraction conduit 2082, towards the lithium extraction assembly 2080 and out of the cell to a metal storage system (not shown).

In some embodiments, electrolyzed metal is produced below the level of the catholyte. Advantageously, the density difference between the metal and salt bath creates differential head that pushes the metal into the lithium metal extraction assembly and supplies the necessary differential pressure to partially or fully push the metal out of the electrolyzer.

Application of a vacuum can lead to infiltration of the gas space by air or anode gases, resulting in conversion of the lithium metal to lithium oxide or lithium carbonate according to equation 9 or reaction 10, resulting in a reduction of current efficiency. This may be prevented by supplying a small flow of inert shielding gas into a gas head space within each cathode compartment, such as argon, helium, or dry air, through the cathode shielding gas conduits 2100 to displace the reactive gases.

2Li_((l))+O_(2(g))═Li₂O_((s))   [9]

4Li_((l))+CO_(2(g))═C_((s))+2Li₂O_((s))   [10]

In the illustrated example, the electrolyzer apparatus 2002 has a chlorine delivery system 2070 configured to introduce chlorine gas into the catholyte compartments 2022, 2038 when the electrolyzer apparatus 2002 is in use.

In the illustrated example, the cathode mounting apparatus 2078 has a feed port 2086 through which feed material can be introduced into the anolyte compartment 2010. The feed port 2086 is arranged on the cathode mounting apparatus 2078 such that it is removed from the containment vessel 2004 when the cathode mounting apparatus 2078 is removed from the containment vessel 2004. Alternatively, or in addition, feed ports may be provided in the anode mounting apparatuses, or in areas of the electrolyzer roof that are independent of anode or cathode mounting apparatuses.

Optionally, the catholyte compartments 2022, 2038 may be filled with catholyte prior to commencing electrolysis. In some embodiments, this may be accomplished by filling the individual catholyte compartments 2022, 2038 with solidified salt during assembly or the catholyte can be introduced in molten form through suitable separate conduits or the lithium extraction conduit prior to installation of the cathode mounting apparatus 2078. In other embodiments, a filling tube may be used to allow communication between the anolyte compartment and the catholyte compartments 2022, 2038 during apparatus start-up. In the illustrated example, a filling tube 2104 is formed in the shape an inverted “J”, as shown in FIG. 9a and FIG. 7. The filling tube 2104 is positioned so that one end is in communication with the anolyte compartment 2010 and the other end is in the catholyte compartment 2022. The catholyte end of the filling tube 2104 terminates at the elevation of the minimum bath level. The anolyte end of the filling tube 2104 extends below the minimum bath level. In the illustrated example, each catholyte compartment has a filling tube.

Through this arrangement, anolyte/electrolyte can be drawn into each catholyte compartment in situ after installing the cathode mounting apparatuses 2078. In some embodiments, this can be accomplished by applying a vacuum to the lithium extraction assembly 2080. The electrolyte flows into the catholyte compartment 2022 through the filing tube 2104 while the vacuum is applied. The electrolyte level in the catholyte compartment 2022 rises until it reaches the lithium extraction conduit 2082. Preferably, the vacuum level can be controlled such that it is sufficient to bring electrolyte into the catholyte compartment 2022, but not sufficient to pull the electrolyte up through the entire lithium extraction conduit 2082 and into the lithium extraction assembly 2080. By doing so, the catholyte compartments can be filled to the desired level without the need for level sensors or individual filling systems for each catholyte compartment. While shown as a j-shaped conduit, the filling tube may have other configurations in other examples.

While the electrolyzer apparatuses described herein are in use carbon may be formed as a by-product of the desired reactions and may accumulate in certain regions of the electrolyzer apparatuses. Such carbon accumulation may be the result of the transport of carbonate ions across the membrane and into the cathode compartment such as by the lithium carbonate-containing anolyte being drawn into the cathode compartment, despite the presence of the cathode housings. This may be undesirable because it may reduce the current efficiency and/or may cause elemental carbon sludge and lithium oxide build-up in the catholyte.

To help reduce the undesirable carbon formation, chlorine gas can be bubbled through the catholyte upon initial filling, and at other suitable times, to react the lithium carbonate to carbon dioxide and lithium chloride. This can be accomplished through a temporary or permanent tube inserted into the membrane. In some embodiments, the bubbling can be continued at a rate sufficient to react with any lithium carbonate diffusing through the porous membrane, thereby slowing or eliminating carbon sludge and/or lithium oxide fouling of the catholyte and maintaining the concentration of carbonate ions below about 100 ppm, and mere preferably below 50 ppm.

Similarly, excess chlorine can be bubbled into the catholyte or used as a shielding gas to fill or at least partially fill the headspace within the vessel 2004, which may help exclude oxygen from the headspace. This chlorine gas can react with any metal produced on the exterior of the gas capture hood 2074 or cathode stub 2098 and convert it back into lithium chloride. This may protect the porous membranes 2028, 2044 from attack by lithium metal and help reduce the accumulation of lithium metal outside the gas capture hood 2074. This may allow the cathode mounting apparatus 2078 to be used for longer before maintenance is required.

Optionally, the electrolyzer apparatus 2002 can be equipped with cooling and/or heating means to adjust the heat balance of the electrolyte. Such cooling or heating means can be used to adjust the heat balance in response to various conditions. For example, as the anode carbon is consumed, the anode-to-cathode distance increases, which can cause additional heat to be generated in the electrolyte, leading to an increase in the temperature of the electrolyte bath. This can be balanced by supplying additional cooling, thereby allowing the electrolyzer apparatus to tolerate larger changes in anode-to-cathode spacing. It may also allow larger anodes to be used, thereby reducing the time between anode replacement.

Use of cooling and/or heating means may also allow the temperature of the electrolyte bath to be set independently of the current and anode-to-cathode distances. This means that the saturation concentration of lithium carbonate in the bath can be better controlled, thereby allowing an inventory of undissolved lithium carbonate to be maintained in the electrolyzer without affecting the concentration available for electrolysis and, if needed, allowing it to be rapidly deployed.

In some embodiments, cooling elements such as cast blocks, cast-in conduits, or channels may be embedded in the lining (walls, floor, roof, or any combination thereof) of the electrolyzer apparatus. A cooling medium, for example, water, air, other gases, molten salts or ionic fluids, can be made to circulate by forced or natural convection through the cooling elements, where it can extract heat and remove it from the electrolyzer apparatus to the atmosphere or some other heat sink or heat exchanger.

In some embodiments, heating elements such as cast blocks or cast-in conduits may embedded in the lining (walls, floor, roof, or any combination thereof) of the electrolyzer apparatus. A heating medium, for example, steam air, combustion gases, molten salts, or ionic fluids, can be made to circulate by forced or natural convection through a heat source, and then made to pass through heating elements, where it heats the electrolyzer.

In other embodiments, electrical heating elements may be mounted in the lining of the electrolyzer (walls, floor, roof, or any combination thereof) or heating or cooling elements may be suspended from the roof or mounted in place of one or more anode or cathode mounting apparatuses and immersed in the electrolyte bath.

Alternatively, the electrolyte bath may be removed from the electrolyzer apparatus and circulated to a heat exchanger where it can be cooled or heated by another cooling or heating element to the desired temperature and returned to the electrolyzer bath.

FIGS. 11a and 11b illustrate a portion of alternative embodiment of an electrolyzer apparatus that is generally analogous to electrolyzer apparatus 2000, and in which analogous features are identified using like reference characters indexed by 3000. In this example the cathode mounting apparatus 3078 includes a cathode structural member 3096 along with a cathode electrical connector 3084, cathode stubs 3098, the cathode 3030, membrane 3028 defining the catholyte compartment 3022 and cathode roof lining elements 3102, each of which are directly or indirectly affixed to the cathode structural member 3096.

In this illustrated example, metal can be collected in gas-tight metal collection elements 3106, in the form of open-bottomed hoods, located in, or forming the top of, the cathode compartments 3022 and partially or fully submerged below the level of the electrolyte. The depth of submergence can be selected such that the density difference between the metal and molten salt electrolyte generates sufficient head to push the metal up and into the lithium extraction assembly, including lithium metal extraction conduit 3082. The depth can be arranged such that the head is sufficient to drive the metal completely out of the cell, or a small vacuum may be used to withdraw the metal. In this arrangement, shielding gas is not required to protect the metal from reactions 9 and 10.

A test campaign was completed on one example of a full-scale electrolyzer according to the teachings described herein. The cell in the test electrolyzer was equipped with two electrode pairs disposed in a common anolyte bath, each having an anode, cathode and cathode housing/membrane as described herein, and a power supply capable of delivering several thousand amps of current. The cell was fed with lithium carbonate feed material and operated over several hours under conditions described herein, during which period lithium metal was produced and collected.

FIG. 12 is a plot showing data gathered during this test campaign, and specifically shows current density, applied voltage and gas analysis over a span of five hours, during which the current was increased in steps, producing periods of operation at 0.2 A/cm², 0.6 A/cm², and 1.25 A/cm², with the majority of the testing time being spent operating at the highest current density.

Despite operating the electrolyzer at different applied voltages between 10-15V for the majority of the time during testing, no chlorine gas was detected in any of the gas samples taken, nor was any chlorine detected in an ambient atmosphere monitor that was placed near the roof of the cell, demonstrating that the apparatus constructed in accordance with the teachings herein can be operated at relatively high current density, and at a relatively high process intensity, with the attendant advantages of having relatively lower capital and operating costs as compared to some conventional systems.

In another example, during a test campaign completed on a full-scale electrolyzer apparatus/cell equipped with graphite anodes approximately 23 kAh of charge were passed between a pair of electrode faces. The anode was removed and carbon loss from the anode was measured based on a comparison to the baseline condition of the anode. This was compared against the calculated stoichiometric carbon loss expected for the given charge transfer. The results of this comparison are tabulated in Table 2 below, and show that the scale electrolyzer apparatus based on the teachings described herein reduces consumption of carbon by approximately 25% as compared to the stoichiometric value. This shows some relatively improved economic characteristics compared to some conventional systems.

TABLE 2 Total Charge Passed 23.4 kAh Total Carbon Loss 1.9 kg Expected Theoretical 112 g/kAh Carbon Loss Actual Carbon Loss 82 g/kAh

In another example, an electrolyzer according to the teachings described herein was operated using a metal oxide semi-inert anode for a period of 12 hrs. Metal product samples obtained from the apparatus were analyzed using glow discharge mass spectrometry (GDMS). The analysis results showing product composition in mass percent are presented in Table 3. Despite apparent contamination of the sample with electrolyte (as indicated by the relatively high chlorine content), the results indicate that a good quality crude metal was produced.

TABLE 3 Li  98.1% Na   0.7% Ca 0.0029% K  0.07% Fe 0.0035% Cl    1% Other   0.1% Total  100.0%

While this invention has been described with reference to illustrative embodiments and examples, the description is not intended to be construed in a limiting sense. Thus, various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments.

All publications, patents and patent applications referred to herein are incorporated by reference in their entirety to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference in its entirety. 

What is claimed is:
 1. A process for producing lithium metal from lithium carbonate using an electrolyzer apparatus having a containment vessel defining an anolyte compartment containing a first anode and a second anode submerged in a common anolyte bath comprising chloride salts, the process comprising: a) providing a first cathode housing in the anolyte bath proximate the first anode, the first cathode housing defining a first catholyte compartment containing a first cathode and a molten salt catholyte and being at least partially bounded by a first primary transfer portion disposed between the first cathode and first anode and comprising a first porous membrane configured to permit migration of lithium ions and resist migration of carbonate ions; b) providing a second cathode housing in the anolyte bath proximate the second anode, the second cathode housing defining a second catholyte compartment containing a second cathode and the molten salt catholyte and being at least partially bounded by a second primary transfer portion disposed between the second cathode and second anode and comprising a second porous membrane configured to permit migration of lithium ions and resist migration of carbonate ions; c) introducing a lithium carbonate feed material into the anolyte bath; d) applying an electric overpotential that is sufficient to initiate electrolysis of lithium carbonate feed material and is substantially greater than the equilibrium potential of lithium chloride between the first anode and the first cathode and between the second anode and the second cathode, thereby electrolyzing the lithium carbonate feed material; e) transferring lithium ions from the anolyte bath into the first catholyte compartment through the first primary transfer portion and resisting the transfer of carbonate ions from the anolyte bath into the first catholyte compartment; f) transferring lithium ions from the anolyte bath into the second catholyte compartment through the second primary transfer portion and resisting the transfer of carbonate ions from the anolyte bath into the second catholyte compartment; and g) converting the lithium ions into lithium metal.
 2. The process of claim 1, further comprising introducing chlorine gas into the first catholyte compartment via a chlorine delivery system, reacting the chlorine gas with the lithium carbonate to form lithium chloride (LiCl) and carbon dioxide.
 3. The process of claim 1, wherein a carbonate ion concentration in the catholyte within the first catholyte compartment is less than in the anolyte bath.
 4. The process of claim 3, carbonate ion concentration in first catholyte compartment is less than about 100 ppm.
 5. The process of any one of claims 1 to 4, further comprising inhibiting carbon or lithium oxide fouling of the first cathode by introducing chlorine gas into the catholyte in the first cathode compartment.
 6. The process of claim 1, further comprising maintaining a current density of between about 0.75 A/cm² and about 4 A/cm² between the first anode and first cathode and between the second anode and second cathode.
 7. The process of claim 6, wherein the current density is at least about 1.2 A/cm².
 8. The process of claim 1, further comprising maintaining a concentration of lithium carbonate of at least 0.1 mol % in the anolyte bath.
 9. The process of claim 8, further comprising maintaining a concentration of lithium carbonate of at least 0.5 mol % in the anolyte bath.
 10. The process of claim 1, further comprising extracting anode gases generated proximate the first anode via an anode gas extraction apparatus and introducing additional lithium carbonate feed material into the anolyte bath when a concentration of chlorine gas in the anodes gases exceeds a predetermined monitoring threshold.
 11. The process of any one of claims 1 to 10, wherein a quantity of carbon that is required per unit of lithium metal produced is less than about 0.4 kg C/kg Li.
 12. The process of any one of claims 1 to 11, further comprising maintaining at least one of the anolyte and the catholyte at a temperature that is greater than 375° C., or preferably is greater than about 400° C.
 13. The process of claim 12, further comprising maintaining the at least one of the anolyte and the catholyte at a temperature that is between about 450° C. and about 700° C.
 14. The process of any one of claims 1 to 13, wherein the anolyte and the catholyte each comprise molten LiCl and KCl.
 15. The process of any one of claims 1 to 14, wherein the electrolyzer apparatus further comprises a first cathode mounting apparatus extending over an open upper end of the containment vessel and supporting at least the first cathode, and wherein the first cathode mounting apparatus is removable from the containment vessel and the first cathode is removed with the first cathode mounting apparatus while the anolyte bath remains contained within the anolyte compartment.
 16. The process of claim 15, wherein the first cathode mounting apparatus comprises a first feed port through which lithium carbonate is introduced into the anolyte bath and wherein removing the first cathode mounting apparatus simultaneously removes the first cathode and the first feed port from the containment vessel.
 17. A molten salt, membrane electrolyzer apparatus for the production of lithium metal from lithium carbonate via an electrolysis process, the apparatus comprising: a) a containment vessel defining an anolyte compartment containing a molten salt anolyte bath comprising chloride salts and a lithium carbonate (Li₂CO₃) feed material; b) a first electrode assembly comprising: i. a first anode extending into the anolyte compartment and in fluid contact with the molten salt anolyte bath; ii. a first cathode housing proximate the first anode within the anolyte compartment and in fluid contact with the molten salt anolyte bath, the first cathode housing defining a first catholyte compartment containing a molten salt catholyte comprising chloride salts and being at least partially bounded by a primary transfer portion comprising a first porous membrane configured to permit migration of lithium ions and resist migration of carbonate ions from the anolyte compartment into the first catholyte compartment; iii. a first cathode within the first catholyte compartment, in fluid contact with the catholyte and positioned so that the primary transfer portion is disposed between the first anode and the first cathode; c) a second electrode assembly comprising: i. a second anode extending generally into the anolyte compartment and in fluid contact with the molten salt anolyte bath; ii. a second cathode housing proximate the second anode within the anolyte compartment and in fluid contact with the molten salt anolyte bath, the second cathode housing defining a second catholyte compartment containing a molten salt catholyte comprising chloride salts and being at least partially bounded by a primary transfer portion comprising a second porous membrane configured to permit migration of lithium ions and resist migration of carbonate ions from the anolyte compartment into the second catholyte compartment; iii. a second cathode within the second catholyte compartment in fluid contact with the catholyte and positioned so that the second primary transfer portion is disposed between the second anode and the second cathode; d) a power supply configured to apply an electric potential between at least the first anode and the first cathode that that is greater than the electric potential required to initiate electrolysis of the lithium carbonate feed material and is substantially greater than the equilibrium potential of lithium chloride.
 18. The apparatus of claim 17, wherein the containment vessel comprises an open upper end and wherein the first anode, first cathode, second anode and second cathode extend downwardly through the open upper end into the anolyte bath.
 19. The apparatus of claim 17, wherein the electric potential between the first anode and the first cathode is at least 4V.
 20. The apparatus of claim 18, wherein the electric potential between the first anode and the first cathode is at least 7V and may be about 10V.
 21. The apparatus of claim 18, wherein the electric potential between the first anode and the first cathode is at least 10V.
 22. The apparatus of any one of claims 1 to 21, wherein the first electrode assembly operates at current density of between about 1 A/cm² and about 4 A/cm².
 23. The apparatus of claim 22, wherein the first electrode assembly operates at current density of about 1.2 A/cm².
 24. The apparatus of any one of claims 1 to 23, wherein the first anode comprises a generally planar plate having a first anode active surface facing the first cathode, and the first cathode comprises a generally planar plate that is substantially parallel to the first anode and having a first cathode active surface opposite and facing the anode active surface.
 25. The apparatus of claim 24, wherein the first cathode active surface is between about 50% and about 200% of the first anode active surface, and preferably is between about 80% and about 120% of the anode active surface, and more preferably is substantially the same as the anode active surface.
 26. The apparatus of any one of claims 1 to 25, wherein the second electrode assembly is adjacent the first electrode assembly such that the first cathode is disposed between and is generally equally spaced between the first anode and the second anode, and wherein an electric potential that is sufficient to initiate electrolysis of lithium carbonate and is greater than the equilibrium potential of lithium chloride is applied between the first cathode and the second anode.
 27. The apparatus of claim 26, wherein the first cathode housing comprises a secondary transfer portion disposed between the first cathode and the second anode and comprising a porous membrane to permit migration of lithium ions from the anolyte compartment into the first catholyte compartment and resisting the migration of carbonate ions from the anolyte compartment into the first catholyte compartment.
 28. The apparatus of claim 27, wherein the first cathode housing is formed at least substantially entirely from the porous membrane.
 29. The apparatus of claim 28, wherein at least some regions of the first cathode housing outside the primary transfer portion and the secondary transfer portion are treated to inhibit the transmission of ions through the regions of the first cathode housing outside the primary transfer portion and the secondary transfer portion.
 30. The apparatus of claim 29, wherein the least some regions of the first cathode housing outside the primary transfer portion and the secondary transfer portion are coated or impregnated with an ion blocking material.
 31. The apparatus of claim 17 wherein the first cathode housing is formed east substantially entirely from the porous membrane.
 32. The apparatus of claim 31, wherein at least some regions of the first cathode housing outside the primary transfer portion are treated to inhibit the transmission of ions through the regions of the first cathode housing outside the primary transfer portion.
 33. The apparatus of claim 32, wherein the least some regions of the first cathode housing outside the primary transfer portion are coated or impregnated with an ion blocking material.
 34. The apparatus of any one of claims 17 to 33, wherein the porous membrane is formed from a ceramic material and having an average pore size of between about 0.1 and about 100 microns, and preferably has a maximum pore size of about 1 micron and average pore size less than about 0.5 microns.
 35. The apparatus of any one of claims 17 to 34, wherein a concentration of carbonate ions within the first catholyte compartment is less than about 100 ppm while the apparatus is in use.
 36. The apparatus of any one of claims 17 to 35, wherein a concentration of carbonate ions within the first catholyte compartment is less than a concentration of carbonate ions within the anolyte compartment.
 37. The apparatus of any one of claims 17 to 36, wherein the first anode is removable from the anolyte compartment independently of the first cathode housing and the first cathode.
 38. The apparatus of any one of claims 17 to 37 wherein the first anode is removable from the anolyte compartment independently of the second anode.
 39. The apparatus of any one of claims 17 to 38, wherein the first anode is removable from the anolyte compartment without draining the molten salt anolyte bath from the anolyte compartment.
 40. The apparatus of any one of claims 17 to 39, further comprising a chlorine delivery system configured to introduce chlorine gas into the first catholyte compartment while the apparatus is in use.
 41. The apparatus of claim 40, wherein the chlorine gas reacts with Li₂CO₃ present within the first catholyte compartment to produce LiCl and carbon dioxide, thereby inhibiting carbon or lithium oxide fouling of the first cathode.
 42. The apparatus of claim 40 or 41, wherein the chlorine gas reacts with excess lithium within the first catholyte compartment thereby inhibiting damage to the membrane.
 43. The apparatus of any one of claims 17 to 42, further comprising a gas extraction apparatus configured to capture product gases formed adjacent the first anode and convey the product gases away from the containment vessel.
 44. The apparatus of any one of claims 17 to 43, wherein the anolyte bath is at a temperature that is at least about 375° C., or preferably is at least about 400° C.
 45. The apparatus of claim 44, wherein the anolyte bath is at a temperature of between about 450° C. and about 700° C.
 46. The apparatus of any one of claims 17 to 45, wherein the first electrode assembly further comprises an anode mounting apparatus extending over the upper end of the containment vessel in a first direction and from which the first anode is suspended, and wherein the anode mounting apparatus is detachable from the containment vessel whereby the first anode is removed from the anolyte compartment.
 47. The apparatus of claim 46, wherein the first anode is detachably connected to the anode mounting apparatus.
 48. The apparatus of claim 46, wherein the anode mounting apparatus further comprises an electrical connector that electrically connects the first anode to the power supply when the anode mounting apparatus is attached to the containment vessel and wherein the electrical connection between the first anode and the power supply is interrupted when the anode mounting apparatus is detached from the containment vessel.
 49. The apparatus of claim 46, wherein the anode mounting apparatus further comprises an insulating layer disposed between the anolyte chamber and the electrical connector to inhibit heat transfer from the molten salt anolyte bath to the electrical connector when the apparatus is in use, and wherein the insulating lining is removable with the anode mounting apparatus.
 50. The apparatus of any one of claims 46 to 49, wherein the anode mounting apparatus further comprises a gas extraction apparatus having a gas capture hood positioned above the first anode and configured to capture product gases formed adjacent the first anode and bubbling out of the molten salt anolyte bath and a gas removal conduit extending from the gas capture hood and configured to convey the product gases away from the containment vessel, wherein at least a portion of the gas extraction apparatus is removable with the anode mounting apparatus.
 51. The apparatus of claim 50, wherein the gas capture hood is electrically isolated from the first anode.
 52. The apparatus of any one of claims 46 to 51, wherein the first electrode assembly further comprises a cathode mounting apparatus extending over the upper end of the containment vessel in the first direction and from which the first cathode is suspended, and wherein the cathode mounting apparatus is detachable from the containment vessel whereby the first cathode is removed from containment vessel with the cathode mounting apparatus.
 53. The apparatus of claim 52, wherein the first cathode housing is suspended from the cathode mounting apparatus whereby the first cathode housing is removed from the containment vessel with the cathode mounting apparatus.
 54. The apparatus of claim 52 or 43, wherein the cathode mounting apparatus further comprises a lithium extraction assembly that includes a lithium extraction conduit that extends from an upper end proximate the cathode mounting apparatus to a lower end that disposed within the first catholyte compartment to extract lithium metal that collects in the catholyte, and wherein the lithium extraction conduit is removed from the containment vessel with the cathode mounting apparatus.
 55. The apparatus of any one of claims 52 to 54, wherein the cathode mounting apparatus further comprises an electrical connector that electrically connects the first cathode to the power supply when the cathode mounting apparatus is attached to the containment vessel and wherein the electrical connection between the first cathode and the power supply is interrupted when the cathode mounting apparatus is detached from the containment vessel.
 56. The apparatus of any one of claims 52 to 55, wherein at least one feed port is provided in the cathode mounting apparatus through with the feed material can be introduced into the anolyte compartment.
 57. The apparatus of claim 56, wherein the at least one feed port is removable from the containment vessel with the cathode mounting apparatus.
 58. The apparatus of any one of claims 52 to 57, further comprising a plurality of cathode mounting apparatuses and anode mounting apparatuses in an alternating arrangement and wherein adjacent ones of the cathode mounting apparatuses and anode mounting apparatuses cooperate to cover substantially the entire upper end of the containment vessel.
 59. The apparatus of any one of claims 17 to 58, further comprising a filling tube fluidly connecting the anolyte compartment and the first catholyte compartment whereby anolyte from the anolyte bath can be drawn into the first catholyte compartment when a vacuum is applied to the first catholyte compartment.
 60. The apparatus of any one of claims 17 to 59, wherein Li₂CO₃ within the anolyte bath reacts with Cl₂ produced within the anolyte compartment, thereby converting it to LiCl, CO₂ and O₂and supressing the emission of Cl₂ from the containment vessel.
 61. The apparatus of any one of claims 17 to 60, wherein a quantity of carbon required per unit of lithium metal produced is less than about 0.4 kg C/kg Li.
 62. The apparatus of any one of claims 17 to 61, wherein a concentration of dissolved lithium carbonate in the anolyte within the anolyte compartment is greater than 0.1 mol % or may be greater about 1 mol %.
 63. The apparatus of claim 62, wherein the concentration of dissolved lithium carbonate concentration of dissolved lithium carbonate in the anolyte within the anolyte compartment is greater than 0.5 mol %.
 64. The apparatus of any one of claims 17 to 63, wherein a CO2/O2 ratio in an off-gas produced at the anode is between about 2 and about 2.5.
 65. The apparatus of any one of claims 17 to 64, wherein the first porous membrane is formed from a ceramic material and having an average pore size of between about 0.1 and about 100 microns, and preferably has a maximum pore size of about 1 micron and average pore size less than about 0.5 microns.
 66. The apparatus of any one of claims 17 to 65, wherein the first porous membrane has an open porosity of between 10-80%, and more preferably between 30-60%.
 67. The apparatus of any one of claims 17 to 66, wherein the first porous membrane is substantially rigid.
 68. The apparatus of any one of claims 17 to 67, further comprising: a) a third electrode assembly comprising: i. a third anode extending into the anolyte compartment and in fluid contact with the molten salt anolyte bath; ii. a third cathode housing proximate the third anode within the anolyte compartment and in fluid contact with the molten salt anolyte bath, the third cathode housing defining a third catholyte compartment containing a molten salt catholyte comprising chloride salts and being at least partially bounded by a primary transfer portion comprising a third porous membrane configured to permit migration of lithium ions and resist migration of carbonate ions from the anolyte compartment into the third catholyte compartment; iii. a third cathode within the third catholyte compartment, in fluid contact with the catholyte and positioned so that the primary transfer portion is disposed between the third anode and the third cathode; b) a fourth electrode assembly comprising: i. a fourth anode extending generally into the anolyte compartment and in fluid contact with the molten salt anolyte bath; ii. a fourth cathode housing proximate the fourth anode within the anolyte compartment and in fluid contact with the molten salt anolyte bath, the fourth cathode housing defining a fourth catholyte compartment containing a molten salt catholyte comprising chloride salts and being at least partially bounded by a primary transfer portion comprising a fourth porous membrane configured to permit migration of lithium ions and resist migration of carbonate ions from the anolyte compartment into the fourth catholyte compartment; iii. a fourth cathode within the fourth catholyte compartment in fluid contact with the catholyte and positioned so that the fourth primary transfer portion is disposed between the fourth anode and the fourth cathode.
 69. A molten salt, membrane electrolyzer apparatus for the production of lithium metal from lithium carbonate via an electrolysis process, the apparatus comprising: a) a containment vessel defining an anolyte compartment containing a molten salt anolyte bath, the anolyte bath comprising chloride salts and more than about 0.1 mol % lithium carbonate (Li₂CO₃) feed material; b) a plurality of electrode assemblies spaced apart from each other and extending into the anolyte compartment, each electrode assembly comprising: i. a cathode housing in fluid contact with the molten salt anolyte bath, the cathode housing defining a catholyte compartment containing a molten salt catholyte comprising chloride salts and being at least partially bounded, by a primary transfer portion comprising a porous membrane configured to permit migration of lithium ions and resist migration of carbonate ions from the anolyte compartment into the catholyte compartment; ii. a cathode positioned within the catholyte compartment, in fluid contact with the catholyte and having an active surface; and iii. an anode in contact with the molten salt anolyte bath and proximate the cathode housing, the anode having an active surface that is substantially equidistant from the active surface of the cathode and being positioned so that the primary transfer portion of the membrane is disposed between the active surface of the anode and the active surface of the cathode; and c) a power supply configured to apply an electric potential to each electrode assembly that is greater than the electric potential required to initiate electrolysis of the lithium carbonate feed material.
 70. The apparatus of claim 69, wherein the plurality of electrode assemblies comprises at least ten electrode assemblies arranged in an array within the anolyte compartment.
 71. The apparatus of claim 69 or 70, wherein the anode comprises a substantially planar plate and the cathode comprises a substantially planar plate that is parallel to the anode.
 72. The apparatus of claim 71, wherein the primary transfer portion of porous membrane is substantially planar and is parallel to both the anode and the cathode.
 73. The apparatus of any one of claims 69 to 72, further comprising at least a first and a second anode support apparatus extending across an open upper end of the containment vessel and over the anolyte compartment, the first anode support apparatus supporting at least a first anode and the second anode support apparatus supporting at least a second anode.
 74. The apparatus of claim 73, wherein the first anode support apparatus and the first anode supported thereon are removable from the containment vessel independently from the second anode support apparatus.
 75. The apparatus of claim 74, wherein the first anode support apparatus and the first anode supported thereon are removable while the anolyte bath is contained within the anolyte compartment.
 76. The apparatus of any one of claims 73 to 75, wherein the first anode support apparatus comprises an electrical connector that electrically connects the first anode to the power supply and wherein the electrical connection is interrupted when the first anode support apparatus is removed.
 77. The apparatus of any one of claims 73 to 76, further comprising at least a first cathode support apparatus disposed between the first and second anode support apparatuses, and a second cathode support apparatus on an opposing side of the second anode support, each cathode support apparatus across he open upper end of the containment vessel and over the anolyte compartment, the first cathode support apparatus supporting at least a first cathode proximate the first anode and the second cathode support apparatus supporting at least a second cathode proximate the second anode.
 78. The apparatus of claim 77, wherein the first cathode support apparatus and first cathode supported thereon are removable from the containment vessel independently from the first anode support apparatus.
 79. The apparatus of claim 78, wherein the first cathode support apparatus and first cathode supported thereon are removable from the containment vessel while the anolyte bath is contained within the anolyte compartment.
 80. The apparatus of claim 78 or 79, wherein the first cathode support apparatus comprises an electrical connector that electrically connects the first cathode to the power supply and wherein the electrical connection is interrupted when the first cathode support apparatus is removed.
 81. The apparatus of any one of claims 78 to 80, wherein a first cathode housing surrounding the first cathode is suspended from the first cathode mounting apparatus whereby the first cathode housing is removed from the containment vessel with the first cathode mounting apparatus.
 82. The apparatus of any one of claims 69 to 81, wherein the porous membrane comprises a ceramic material which is non-wetting by lithium metal.
 83. The apparatus of claim 82, wherein the non-wetting ceramic material has an open porosity of between about 30% and about 60%.
 84. The apparatus of any one of claims 69 to 83, wherein a ratio of an area of the active surface of the anode to an area of the active surface of the cathode is between about 0.5 and 2, and more preferably is between 0.8 to 1.2.
 85. The apparatus of any one of claims 69 to 84, further comprising a chlorine delivery system configured to introduce chlorine gas into each catholyte compartment.
 86. The apparatus of claim 85, wherein the chlorine gas reacts with lithium carbonate present within the catholyte to product carbon dioxide and lithium chloride.
 87. The apparatus of any one of claims 69 to 84, wherein the porous membrane is formed from a ceramic material and having an average pore size of between about 0.1 and about 100 microns and preferably has a maximum pore size of about 1 micron and average pore size less than about 0.5 microns.
 88. The apparatus of any one of claims 69 to 87, wherein the electric potential between the anode and the cathode is at least 4V.
 89. The apparatus of claim 88, wherein the electric potential between the anode and the cathode is at least 7V and may be about 10V.
 90. The apparatus of claim 89, wherein the electric potential between the anode and the cathode is at least 10V.
 91. The apparatus of any one of claims 69 to 90, wherein the each electrode assembly operates at current density of between about 1 A/cm² and about 4 A/cm².
 92. The apparatus of claim 91, wherein each electrode assembly operates at current density of about 1.2 A/cm².
 93. The apparatus of any one claims 69 to 92, wherein the power supply configured to apply an electric potential to each electrode assembly that is greater than the equilibrium potential of lithium chloride.
 94. The apparatus of any one of claims 62 to 93, wherein the anolyte bath is at a temperature that is at least about 375° C., or preferably is at least about 400° C., or more preferably may be between about 450° C. and about 700° C. degrees Celsius. 